introduction to chemical reactions assignment

Want to create or adapt books like this? Learn more about how Pressbooks supports open publishing practices.

1.8 Introduction to Chemical Reactions and Equations

Joey Wu and OpenStax

Learning Objectives

• Define terms used to represent chemical reactions including reactants, products, states, coefficients, and stoichiometry, reaction conditions.
• Differentiate between the liquid phase and the aqueous phase

Chemical Reactions

The space shuttle—and any other rocket-based system—uses chemical reactions to propel itself into space and maneuver itself when it gets into orbit. The rockets that lift the orbiter are of two different types. The three main engines are powered by reacting liquid hydrogen with liquid oxygen to generate water. Then there are the two solid rocket boosters, which use a solid fuel mixture that contains mainly ammonium perchlorate and powdered aluminum. The chemical reaction between these substances produces aluminum oxide, water, nitrogen gas, and hydrogen chloride. Although the solid rocket boosters each have a significantly lower mass than the liquid oxygen and liquid hydrogen tanks, they provide over 80% of the lift needed to put the shuttle into orbit—all because of chemical reactions.

Figure 1 . When we think about chemistry, we usually think about chemical reactions, such as combustion.

Chemistry is largely about chemical changes. Indeed, if there were no chemical changes, chemistry as such would not exist! Chemical changes are a fundamental part of chemistry. Because chemical changes are so central, it may be no surprise that chemistry has developed some special ways of presenting them.

What are Chemical Equations?

Chemical equations are how chemists describe chemical reactions, the process by which one form of matter ( reactants ) turn into another form of matter ( products ). Below is the balanced chemical reaction for the combustion of methane (CH 4 ) with oxygen (the reactants) to produce carbon dioxide and water (the products), see Figure 2.

Figure 2 . Reactants and Products of a chemical equation

Law of Conservation of Mass: Balancing Reactions

CO+O 2 → CO 2

(unbalanced equation)

As matter is made of compounds and elements, and the compounds may change, this means the total number of atoms of each element must be conserved. In the equation below, only atoms of carbon are conserved, and so the equation is not balanced. In the equation below, that atoms of each element are conserved, and so it is balanced.

2CO+O 2 = 2CO 2 (balanced equation)

Stoichiometric Coefficients:

Once the reactants and products are written, you are not able to change the subscripts of the compound to balance the chemical reaction without changing the identity of the reactants and products. However, you may use stoichiometric coefficients in front of each chemical entity (molecule or element) to balance the equations.

2H 2 + O 2 -> 2H 2 O

Extension: Catalyst

Catalysts can be understood by looking at the mechanism of a reaction, that is, how it actually proceeds, and can be considered to be chemicals that function as both a reactant and a product. That is, the catalyst reacts with something and form a new chemical, an intermediate, and that intermediate also reacts, and reproduces the catalyst. Catalysts can speed up reactions , or make reactions happen which without the catalyst are so slow that they don’t really happen.

Key Takeaways

• A chemical reaction is a process in which some substances, called reactants, change into different substances, called products.
• All chemical reactions involve both reactants and products. Reactants are substances that start a chemical reaction, and products are substances that are produced in the reaction.
• Chemical equations should be balanced because the total number of atoms from each elements are conserved.

STEM for Educators Copyright © 2022 by Joey Wu and OpenStax is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

Share This Book

• Science Notes Posts
• Contact Science Notes
• Todd Helmenstine Biography
• Anne Helmenstine Biography
• Free Printable Periodic Tables (PDF and PNG)
• Periodic Table Wallpapers
• Interactive Periodic Table
• Periodic Table Posters
• How to Grow Crystals
• Chemistry Projects
• Fire and Flames Projects
• Holiday Science
• Chemistry Problems With Answers
• Physics Problems
• Unit Conversion Example Problems

Chemistry Worksheets

• Biology Worksheets
• Periodic Table Worksheets
• Physical Science Worksheets
• Science Lab Worksheets
• My Amazon Books

Chemistry Worksheets and Handouts (PDF for Printing)

This is a collection of free chemistry worksheets and handouts to print. Most of the printables are PDF files, although some are available as JPG or PNG files. All of these worksheets print cleanly on normal printer paper, plus you can resize them to fit your needs.

Here is a list of worksheets. This site also has articles explaining these topics in detail.

• Label Parts of the Atom [ Google Apps worksheet ][ worksheet PDF ][ worksheet PNG ][ answers PNG ]
• Acid formulas [ PDF ][ Answers ]
• Balancing equations Worksheet #1 [ PDF ][ Answers ] Worksheet #2 [ PDF ][ Answers ] Worksheet #3 [ PDF ][ Answers ] Worksheet #4 [ PDF ][ Answers ]
• Chemical and Physical Changes [ PDF ][ Answers ]
• Chemistry scavenger hunt [ PDF clues ][ Answers ]
• Element names crossword [ PDF ][ Answers ]
• Element symbols – Symbols that make words [ PDF worksheet ][ Answers ]
• Element symbols – Countries of the world [ PDF ][ Answers ]
• More element symbol worksheets
• Homogeneous or Heterogeneous Mixtures [ PDF ][ Answers ]
• Intensive and Extensive Properties [ Worksheet ][ Answer Key ]
• Intrinsic and Extrinsic Properties [ PDF ][ Answers ]
• Ionic and Covalent Compounds (Names and Identification) [ PDF Worksheet ][ Answer Key ]
• Ionic Compound Names and Formulas [ PDF Worksheet ][ Answer Key ]
• Metric to English Unit Conversions [ PDF Worksheet ][ Answer Key ]
• Mixtures [ PDF ][ Answers ]
• Periodic table scavenger hunt [ PDF clues ][ Answers ]
• Reading a meniscus [ PDF ][ Answers ]
• Reading periodic table element information Worksheet #1 [ PDF ][ Answers ] Worksheet #2 [ PDF ][ Answers ]
• Scientific Notation [ PDF ][ Answers ]
• Significant digits Rules [ PDF ][ Answers ] Addition and subtraction [ PDF ][ Answers ] Multiplication and division [ PDF ][ Answers ]
• Types of Chemical Reactions [ Worksheet ][ Answers ]

In addition to these chemistry worksheets, there is a collection of word search puzzles .

Chemistry Handouts

These chemistry handouts illustrate chemistry concepts and offer examples.

• Amino acid side chains [ PDF ]
• Antimatter examples [ PNG ]
• Atom facts [ PNG ]
• Chemical properties [ JPG ]
• Colligative properties [ JPG ]
• Electron configurations [ PDF ]
• Element electronegativities [ PDF ]
• 118 Element Flash Cards [ PDF ]
• Element list [ PDF ]
• Endothermic reactions [ PNG ]
• Error calculations [ JPG ]
• Exothermic reactions [ JPG ]
• Heterogeneous mixtures [ JPG ]
• Hydrocarbon prefixes [ JPG ]
• Ionic compound properties [ PNG ]
• Genetic codons [ PDF ]
• Lewis structures [ JPG ]
• Litmus test [ PNG ]
• Magnetic vs non-magnetic metals [ JPG ]
• Mole ratio [ JPG ]
• Organic vs inorganic [ JPG ]
• Oxidation numbers [ JPG ]
• Periodic table Bingo game [ PDF ]
• pH indicators [ PNG ]
• Physical change [ JPG ]
• Physical properties [JPG ]
• Noble metals [ JPG ]
• Reactants and products [ JPG ]
• RNA vs DNA [ JPG ]
• States of matter [ JPG ]
• Visible spectrum [ JPG ]

Periodic Tables

There’s a printable periodic table for just about any purpose, but some of the most popular are listed here.

• 118 element vibrant periodic table [ PNG ]
• Actinides [ JPG ]
• Blank periodic table [ PDF ]
• Element charges [ JPG ]
• Element density [ PDF ]
• Element electrical conductivity [ PDF ]
• Element state of matter [ PDF ]
• Muted color 118 element periodic table [ PDF ]
• Native elements [ JPG ]
• Valence [ JPG ]

Biology Worksheets and Handouts

Is biology more your thing? We’ve got similar resources for the life sciences, including biology, biochemistry, cell biology, and anatomy.

Chemistry Worksheets Terms of Use

You are welcome to print these resources for personal or classroom use. They may be used as handouts or posters. They may not be posted elsewhere online, sold, or used on products for sale.

This page doesn’t include all of the assets on the Science Notes site. If there’s a table or worksheet you need but don’t see, just let us know!

Related Posts

3.16: Introduction to Chemical Reactions

Chapter 1: introduction to the human body, chapter 2: diagnostic imaging techniques, chapter 3: fundamentals of chemistry, chapter 4: biochemistry of the cell, chapter 5: cells and their components, chapter 6: cell membrane structure and functions, chapter 7: essential cellular processes, chapter 8: tissues of the human body, chapter 9: the integumentary system, chapter 10: bone tissue and the skeletal system, chapter 11: the axial skeleton, chapter 12: the appendicular skeleton, chapter 13: the joints, chapter 14: muscle tissue, chapter 15: the muscular system, chapter 16: the nervous system and nervous tissue, chapter 17: anatomy of the central and peripheral nervous system, chapter 18: functions of the central and peripheral nervous system, chapter 19: the autonomic nervous system, chapter 20: the special senses, chapter 21: the endocrine system.

The JoVE video player is compatible with HTML5 and Adobe Flash. Older browsers that do not support HTML5 and the H.264 video codec will still use a Flash-based video player. We recommend downloading the newest version of Flash here, but we support all versions 10 and above.

A chemical reaction is a process where atoms in one or more substances, known as reactants, change their arrangement by breaking their chemical bonds and forming new bonds to create the products.

Reactions which result in a net release of energy are exergonic, while endergonic reactions are net absorbers of energy.

The biochemical reactions occurring in the human body are categorized as either synthesis or anabolic, such as protein synthesis, decomposition, or catabolic, such as the breakdown of polysaccharides into simple sugars, or exchange reactions, such as the transfer of ATP's phosphate to glucose to form glucose-phosphate.

Many biochemical reactions use enzymes as catalysts to speed up the reaction.

All biochemical reactions progress towards equilibrium — a state where no net change in the concentrations of reactants and products occurs because the forward and reverse reactions are happening at the same rate.

The biochemical reactions provide energy to maintain homeostasis and perform essential functions such as growth and repair.

All chemical reactions begin with a reactant, the general term for one or more substances entering the reaction. Sodium and chloride ions, for example, are the reactants in the production of table salt. One or more substances produced by a chemical reaction are called the product. Chemical reactions follow the law of conservation of mass, which means that matter cannot be created nor destroyed in a chemical reaction. The components of the reactants—the number of atoms and the elements—are all present in the product(s). Similarly, there is nothing in the products that are not present in the reactants.

Chemical reactions require sufficient energy that causes the matter to collide with enough precision and force to break old chemical bonds and form new ones. In general, kinetic energy is the form of energy powering any type of matter in motion. Potential energy is the energy of position or the energy matter possesses because of the positioning or structure of its components. All atoms have kinetic energy as they are always in motion. The energy needed to break the chemical bonds of the reactants and start a reaction is called the activation energy. The concentration and temperature of the reactants can influence the rate of a chemical reaction. 

The convention for writing chemical equations involves placing reactant formulas on the left side of a reaction arrow and product formulas on the right side. By this convention and the definitions of "reactant" and "product," a chemical equation represents the reaction proceeding from left to right. Reversible reactions, however, may proceed in both forward (left to right) and reverse (right to left) directions. When the rates of the forward and reverse reactions are equal, the concentrations of the reactant and product species remain constant over time, and the system is at equilibrium. The relative concentrations of reactants and products in equilibrium systems vary greatly; some systems contain mostly products at equilibrium, some contain mostly reactants, and some contain appreciable amounts of both.

For example, in human blood, excess hydrogen ions (H + ) bind to bicarbonate ions (HCO3 - ), forming an equilibrium state with carbonic acid (H2CO3). If we added carbonic acid to this system, some of it would convert to bicarbonate and hydrogen ions.

However, biological reactions rarely obtain equilibrium because the concentrations of the reactants or products or both are constantly changing, often with one reaction's product a reactant for another. To return to the example of excess hydrogen ions in the blood, forming carbonic acid will be the reaction's major direction. However, the carbonic acid can also leave the body as carbon dioxide gas (via exhalation) instead of converting back to bicarbonate ion; this drives the reaction to the right by the law of mass action. These reactions are important for maintaining homeostasis in our blood.

This text is adapted from Openstax, Anatomy and Physiology 2e, Section 2.3: Chemical Reactions , Openstax, Chemistry 2e, Section 13.1: Chemical equilibria and Openstax, Biology 2e, Section 2.1: Atoms, Isotopes, Ions and Molecules: The Building Blocks

Get cutting-edge science videos from J o VE sent straight to your inbox every month.

mktb-description

We use cookies to enhance your experience on our website.

By continuing to use our website or clicking “Continue”, you are agreeing to accept our cookies.

Introduction to Chemical Reactions

Article objectives.

• The objective of this article is to explain the concept of chemical reactions and the types of chemical reactions.

Introduction

One of the most fundamental concepts of chemistry is something known as the Law of Conservation of Matter , that states that atoms are never introduced or destroyed. This is what allows chemical reactions to work, where one or more chemicals react in such ways that one or more new chemicals are formed, via the moving of electrons between substances. The chemicals present before the reaction are called reactants (for the obvious reason), and the chemicals present after the reaction are called products . No chemical reaction is a chemical reaction without both of these components.

Introduction to Chemical Equations

On paper, a chemical reaction can be written out in the form of a chemical equation , which shows the reaction taking place. Of course there is always a way to describe the reaction in words too.

Example 1: Write a chemical equation for Magnesium Hydroxide and Sulfuric Acid being mixed together in solution to get Magnesium Sulfate and Water.

Solution: The reactants are written on the left, and the products are written on the right, with an arrow in between.

$$Mg(OH)_2 + H_2SO_4 \rightarrow H_2O + MgSO_4$$

States of Matter

Often, it is a good idea to include states of matter in a chemical equation. A state of matter is the phase of the chemical, so either solid, liquid, or gas. In addition, in chemical equations the phrase aqueous is treated as a state of matter. This refers to a chemical being dissolved in a solution with water.

When placing states of matter in chemical equations, use the following symbols:

\((s)\) for a solid

\((l)\) for a liquid (usually water)

\((g)\) for a gas

\((aq)\) for an aqueous substance

Example 2: Write an equation for a reaction between aqueous Gold Perchlorate and solid Titanium which form solid Gold and aqueous Titanium Perchlorate. Include states of matter.

Solution: Use the information given about the chemicals to write the equation:

$$Au(ClO_4)_3 + Ti \rightarrow Ti(ClO_4)_2 + Au$$

Now add the states of matter.

$$Au(ClO_4)_3(aq) + Ti(s) \rightarrow Ti(ClO_4)_2(aq) + Au(s)$$

As a general rule of thumb, always include the states of matter if they are given.

Single Replacement Reactions

There are many different types of chemical reactions, and they are classified based on a combination of the identity of the reactants and products and how many substances/ions are directly involved in the reaction. A single replacement reaction is a reaction where one substance or ion is moved, and nothing else.

Example 3: Based on the following chemical equation, is the reaction a single replacement reaction? How can you tell? The equation is

$$BaCO_3 + Na \rightarrow Na_2CO_3 + Ba$$

Solution: This is a single replacement reaction. The way we can tell is that only the Carbonate ion (\(CO_3^{2-}\)) is moving, and thus influencing the charges of the Sodium and the Barium.

Example 4: Magnesium Chloride and solid Barium react in a single-replacement reaction. What are the products?

Solution: In a single-replacement reaction, one chemical will be moved between substances. Since Magnesium Chloride is an ionic compound, it will likely be an ion. Seeing Magnesium and Barium in a compound together is uncommon because both of these elements are metals, but Barium Chloride is a perfectly plausible ionic compound, so we have the reaction

$$MgCl_2+Ba \rightarrow BaCl_2+Mg$$

So the products are solid Magnesium and Barium Chloride.

Double Replacement Reactions

The counterpart of single replacement reactions, a double replacement reaction is where two substances or ions are moved/inverted to create new substances. Generally double replacement reactions, at least in first-year courses, will have at least two products.

Example 5: Why is the reaction \(HCl + K \rightarrow KCl + H_2\) not a double replacement reaction?

Solution: Only the Chlorine atoms are being moved, so by definition this cannot be a double replacement reaction. It is actually a single replacement reaction.

Example 6: What is one possible double replacement reaction that could theoretically occur between Aluminum Chromate (\(Al(CrO_4)_3\)) and Magnesium Oxide?

Solution: Two components must be inverted to create a double-replacement reaction. It is perfectly valid to allow these substances to be the anions that are present. Therefore we get a chemical equation of

$$Al(CrO_4)_3 + MgO \rightarrow Mg(CrO_4)_2 + Al_2O_3$$

Synthesis Reactions

A synthesis reaction is where two or more chemicals are combined to create one chemical. Generally, if a reaction is known to be a synthesis reaction, predicting the product(s) are easier compared to single or double replacement reactions.

Example 7: The products of a chemical reaction are Sodium Hydroxide and Acetone. Without knowing the products, how do you know that this is not a synthesis reaction?

Solution: There would only be one product, so this must be a different type of reaction.

In the previous example, even though we could tell that it was not a synthesis reaction, we would need to know the reactants in order to determine what type of reaction it actually was.

Example 8: If \(H_2O_2\) and Chromium metal undergo a synthesis reaction, what is one possible product of the reaction?

Solution: Of course there may be multiple answers, but they all must include Chromium, Hydrogen, and Oxygen. This solution creates an ionic compound; the product \(Cr(OH)_3\) appears perfectly valid, as this is indeed a synthesis reaction by definition. For reference, the equation is shown below:

$$H_2O_2 + Cr \rightarrow Cr(OH)_3$$

Decomposition Reaction

A decomposition reaction is a reaction that is in the reverse process of a synthesis reaction; a chemical decomposes into two or more different chemicals. Sometimes the decomposition will be automatic, and other times a trigger such as heat will be necessary.

Example 9: Carbonic acid decomposes naturally. The decomposition reaction is as follows:

$$H_2CO_3 \rightarrow CO_2 + H_2O$$

Oxidation-Reduction Reactions

An oxidation-reduction reaction is a reaction that meets one of two conditions: 1. Elemental oxygen is a reactant. 2. One substance is oxidized , or has electrons taken away from it, and one substance is reduced , where it gets additional electrons.

An oxidation-reduction reaction, or redox reaction, can at the same time be a single replacement reaction, double replacement reaction, or synthesis reaction.

Example 10a: Classify the following chemical reaction in two ways:

$$Sn + O_2 \rightarrow SnO$$

Solution: One of the reactants is elemental oxygen, so it is a redox reaction. In addition, two substances are combined to create one new one, so it is also a synthesis reaction.

The second half of the example generalizes this reaction.

Example 10b: In Example 10a, the Tin metal is being oxidized into Tin cations. All stable metals can undergo basically the same reaction. Here are some specific ones:

$$Li + O_2 \rightarrow Li_2O$$

$$Ca + O_2 \rightarrow CaO$$

$$Al + 3O_2 \rightarrow Al_2O_3$$

In each of these redox reactions, the metal is oxidized and the oxygen is reduced. This property also applies to transition metals (the stable ones):

$$Zr + O_2 \rightarrow ZrO_2$$

Another type of problem is to determine whether a reaction is a redox reaction. As a rule of thumb, check the charges of the ions--redox reactions generally involve ionic compounds.

Example 11: Is this a redox reaction? Explain why.

$$HNO_3 + Cu(OH)_2 \rightarrow Cu(NO_3)_2 + H_2O$$

Solution: There is no elemental oxygen (although substances with oxygen are abundant; don't let this make you think the reaction is redox). Also, there is nothing being oxidized or reduced. Therefore this is not a redox reaction.

Example 12: In the following chemical equation, the element labeled with a question mark is unknown:

$$Mg? + Na \rightarrow Na? + Mg$$

What might this unknown element be if this reaction is a redox reaction?

Solution: There is no room for elemental oxygen in this reaction. However, the "?" can still be oxygen:

$$MgO + Na \rightarrow Na_2O + Mg$$

Here's why: in this reaction, the Magnesium is reduced and the Sodium is Oxidized. Therefore this is a redox reaction.

Basically any anion would work here. For example, if the question mark actually represents Fluorine:

$$MgF_2 + Na \rightarrow NaF + Mg$$

For the same reason, this is still a redox reaction. Even a polyatomic ion would allow this to be a redox reaction (although polyatomic ions are not pure elements). For example, if the ion is Phosphite:

$$Mg_3(PO_3)_2 + Na \rightarrow Na_3PO_3 + Mg$$

Example 13: What type of reaction is this?

$$Mn_2 O_7+Na_2 SO_3 \rightarrow Mn_2 (SO_3)_7+Na_2O$$

Solution: Two different ions, oxide and sulfite, are interchanged. Therefore this is a double-replacement reaction.

Despite being under "Oxidation-Reduction Reactions," the above reaction is not a redox reaction. None of the charges change (nothing is oxidized or reduced). The presence of oxygen may have made you identify the reaction as redox, but that is incorrect because the oxygen is not elemental; it is the anion in the ionic compound Manganese (VII) Oxide.

Combustion Reactions

A combustion reaction is a subtype of redox reactions where a substance is burned with an oxygen flame. Therefore by definition, all combustion reactions are redox reactions, since they always contain elemental oxygen.

Many combustion reactions include elemental oxygen and a hydrocarbon, a chemical comprising only of Carbon and Hydrogen atoms. By default, these reactions always have two products: carbon dioxide and water. The amounts produced are based on the type of hydrocarbon and how much of each reactant are available.

Example 14: Octane is combusted as follows:

$$C_8H_{18} + O_2 \rightarrow CO_2 + H_2O$$

a. Is this reaction a redox reaction?

b. Is this reaction a synthesis reaction?

c. Would the previous answers change if a different hydrocarbon is used?

a. Elemental oxygen is a reactant, so this reaction is a redox reaction.

b. This is not a synthesis reaction, because there are the same number of products as reactants, so two reactants could not combine to form one product.

c. No; regardless, elemental oxygen is still a reactant, and this does nothing to change the products (only the amounts), so this is still not a synthesis reaction.

A carbohydrate is a chemical with only Carbon, Hydrogen, and Oxygen. Combustion of carbohydrates works the same way as the combustion of hydrocarbons.

Example 15: What are the products when \(C_9H_{16}O_2\) is combusted?

Solution: By inspection of the chemical formula \(C_9H_{16}O_2\), it is obvious this is a carbohydrate. As usual, the products will be \(CO_2\) and \(H_2O\). Here is the chemical equation:

$$C_9H_{16}O_2 + O_2 \rightarrow CO_2 + H_2O$$

<div class="article-example" markdown="1">

**Example 16:** Find and balance an equation for the combustion of \(C_7H_{16}O_4\).

**Solution:** "Combustion" implies the addition of elemental oxygen:

$$C_7H_{16}O_4 + O_2 \rightarrow$$

As with any other combustion reaction,  the products are carbon dioxide and water:

$$C_7H_{16}O_4 + O_2 \rightarrow CO_2 + H_2O$$

Balance the hydrogen first:

$$C_7H_{16}O_4 + O_2 \rightarrow CO_2 + 8H_2O$$

Now balance carbon:

$$C_7H_{16}O_4 + O_2 \rightarrow 7CO_2 + 8H_2O$$

There are \(22\) carbon atoms on the right side, so we need the same number on the left side. With four oxygen atoms included in the carbohydrate, the remaining \(18\) must come from the elemental oxygen, so

$$C_7H_{16}O_4 + 9O_2 \rightarrow 7CO_2 + 8H_2O$$

</div>

The Law of Conservation of Matter stated that new matter could not be introduced or removed from existence, but many of the equations in this article appeared to violate this concept because the amount of each chemical on both sides of the equation was not the same. However, there is a way to balance equations to make this rule followed yet again; this will be discussed in a different article, as it is too big a concept to include here.

• school Campus Bookshelves
• menu_book Bookshelves
• perm_media Learning Objects
• login Login
• how_to_reg Request Instructor Account
• hub Instructor Commons
• Download Page (PDF)
• Download Full Book (PDF)
• Periodic Table
• Physics Constants
• Scientific Calculator
• Reference & Cite
• Tools expand_more
• Readability

selected template will load here

This action is not available.

5.9: Introduction to Chemical Reactions (Summary)

• Last updated
• Save as PDF
• Page ID 15242

To ensure that you understand the material in this chapter, you should review the meanings of the following bold terms in the following summary and ask yourself how they relate to the topics in the chapter.

Scientific laws are general statements that apply to a wide variety of circumstances. One important law in chemistry is the law of conservation of matter , which states that in any closed system, the amount of matter stays constant.

Chemical equations are used to represent chemical reactions . Reactants change chemically into products . The law of conservation of matter requires that a proper chemical equation be balanced . Coefficients are used to show the relative numbers of reactant and product molecules.

In stoichiometry , quantities of reactants and/or products can be related to each other using the balanced chemical equation. The coefficients in a balanced chemical reaction are used to devise the proper ratios that relate the number of molecules of one substance to the number of molecules of another substance.

Chemical reactions can be classified by type. Combination reactions (also called composition reactions ) make a substance from other substances. Decomposition reactions break one substance down into multiple substances. Combustion reactions combine molecular oxygen with the atoms of another reactant.

Oxidation reactions are reactions in which an atom loses an electron. Reduction reactions are reactions in which an atom gains an electron. These two processes always occur together, so they are collectively referred to as oxidation-reduction (or redox ) reactions . The species being oxidized it called the reducing agent , while the species being reduced is the oxidizing agent . Alternate definitions of oxidation and reduction focus on the gain or loss of oxygen atoms, or the loss or gain of hydrogen atoms. Redox reactions are easily balanced if the overall reaction is first separated into half reactions , which are individually balanced.

Oxidation-reduction reactions are common in organic and biological chemistry. Respiration , the process by which we inhale and metabolize oxygen, is a series of redox reactions. In the absence of oxygen, redox reactions still occur in a process called anaerobic metabolism . Antioxidants such as ascorbic acid also play a part in the human diet, acting as reducing agents in various biochemical reactions. Photosynthesis , the process by which plants convert water and carbon dioxide to glucose, is also based on redox reactions.

Module 2: Chemistry of Life

Introduction to chemical reactions, understand basic chemical reactions.

In this outcome, we will discuss chemical bonds and reactions.

What You’ll Learn to Do

• Identify the components of simple chemical reactions
• Differentiate between catabolic and anabolic reactions
• Identify enzymes and their role in chemical reactions

Learning Activities

The learning activities for this section include the following:

• Chemical Reactions and Molecules
• Anabolic and Catabolic Pathways
• Self Check: Chemical Reactions
• Introduction to Chemical Reactions. Authored by : Shelli Carter and Lumen Learning. Provided by : Lumen Learning. License : CC BY: Attribution

Introduction

Chapter outline.

Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter. Societies at all levels of development could not function without the energy released by chemical reactions. In 2012, about 85% of US energy consumption came from the combustion of petroleum products, coal, wood, and garbage. We use this energy to produce electricity (38%); to transport food, raw materials, manufactured goods, and people (27%); for industrial production (21%); and to heat and power our homes and businesses (10%). 1 While these combustion reactions help us meet our essential energy needs, they are also recognized by the majority of the scientific community as a major contributor to global climate change.

Useful forms of energy are also available from a variety of chemical reactions other than combustion. For example, the energy produced by the batteries in a cell phone, car, or flashlight results from chemical reactions. This chapter introduces many of the basic ideas necessary to explore the relationships between chemical changes and energy, with a focus on thermal energy.

• 1 US Energy Information Administration, Primary Energy Consumption by Source and Sector, 2012 , http://www.eia.gov/totalenergy/data/monthly/pdf/flow/css_2012_energy.pdf. Data derived from US Energy Information Administration, Monthly Energy Review (January 2014).

As an Amazon Associate we earn from qualifying purchases.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Access for free at https://openstax.org/books/chemistry-2e/pages/1-introduction

• Authors: Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD
• Publisher/website: OpenStax
• Book title: Chemistry 2e
• Publication date: Feb 14, 2019
• Location: Houston, Texas
• Book URL: https://openstax.org/books/chemistry-2e/pages/1-introduction
• Section URL: https://openstax.org/books/chemistry-2e/pages/5-introduction

© Jan 8, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.

• school Campus Bookshelves
• menu_book Bookshelves
• perm_media Learning Objects
• login Login
• how_to_reg Request Instructor Account
• hub Instructor Commons

Margin Size

• Download Page (PDF)
• Download Full Book (PDF)
• Periodic Table
• Physics Constants
• Scientific Calculator
• Reference & Cite
• Tools expand_more
• Readability

selected template will load here

This action is not available.

5: Introduction to Chemical Reactions

• Last updated
• Save as PDF
• Page ID 15924

Chemical change is a central concept in chemistry. The goal of chemists is to know how and why a substance changes in the presence of another substance or even by itself. Because there are tens of millions of known substances, there are a huge number of possible chemical reactions. In this chapter, we will find that many of these reactions can be classified into a small number of categories according to certain shared characteristics.

• 5.0: Prelude to Introduction to Chemical Reactions Although yeast has been used for thousands of years, its true nature has been known only for the last two centuries. Yeasts are single-celled fungi. About 1,000 species are recognized, but the most common species is Saccharomyces cerevisiae, which is used in bread making. Other species are used for the fermentation of alcoholic beverages. Some species can cause infections in humans.
• 5.1: The Law of Conservation of Matter One scientific law that provides the foundation for understanding in chemistry is the law of conservation of matter. It states that in any given system that is closed to the transfer of matter (in and out), the amount of matter in the system stays constant. A concise way of expressing this law is to say that the amount of matter in a system is conserved. The amount of matter in a closed system is conserved.
• 5.2: Chemical Equations Chemical reactions are represented by chemical equations that list reactants and products. Proper chemical equations are balanced; the same number of each element’s atoms appears on each side of the equation.
• 5.3: Quantitative Relationships Based on Chemical Equations A balanced chemical equation not only describes some of the chemical properties of substances—by showing us what substances react with what other substances to make what products—but also shows numerical relationships between the reactants and the products. The study of these numerical relationships is called stoichiometry.  A balanced chemical equation gives the ratios in which molecules of substances react and are produced in a chemical reaction.
• 5.4: Some Types of Chemical Reactions Although there are untold millions of possible chemical reactions, most can be classified into a small number of general reaction types. Classifying reactions has two purposes: it helps us to recognize similarities among them, and it enables us to predict the products of certain reactions. A particular reaction may fall into more than one of the categories that we will define in this book.
• 5.5: Oxidation-Reduction (Redox) Reactions Chemical reactions in which electrons are transferred are called oxidation-reduction, or redox, reactions. Oxidation is the loss of electrons. Reduction is the gain of electrons. Oxidation and reduction always occur together, even though they can be written as separate chemical equations.
• 5.6: Redox Reactions in Organic Chemistry and Biochemistry Redox reactions are common in organic and biological chemistry, including the combustion of organic chemicals, respiration, and photosynthesis.
• 5.E: Introduction to Chemical Reactions (Exercises)
• 5.S: Introduction to Chemical Reactions (Summary) To ensure that you understand the material in this chapter, you should review the meanings of the following bold terms in the following summary and ask yourself how they relate to the topics in the chapter.

http://en.Wikipedia.org/wiki/Exother...teReaction.jpg