Unit B Lesson 12: Chemical Reactions and Word Equations
Completion requirements
Unit B Lesson 12: Chemical Reaction Types
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Learning Targets |
Big Question: How do I write chemical reactions in a word equation?
Chemical reactions occur when reactants undergo a chemical change to form new chemical products. No new matter is created. Like building a Lego plane out of a Lego boat kit, all of the same matter is rearranged to form something different.
Chemical reactions occur when reactants undergo a chemical change to form new chemical products. No new matter is created. Like building a Lego plane out of a Lego boat kit, all of the same matter is rearranged to form something different.
At the end of this inquiry, you should be able to answer the following questions:
- What is the difference between an exothermic reaction and an endothermic reaction?
- How is a chemical reaction represented as a word equation?
- On what side of a word equation should the reactants and/or products be placed?
- What are the three chemical reactions involving oxygen?
Pages 156 to 158 and page 160 in your textbook will help you answer these questions about the types of chemical reactions.
Periodic Table links:
Introduction
In lesson 6, you learned that hydrogen has a lower atomic mass than helium, so hydrogen should float more easily in air. And, in fact, it does. So why do we buy helium balloons instead of hydrogen balloons for our parties? Elements and compounds have
properties that make their use good or bad in a variety of situations. How they react with other chemicals and in different situations is one of those properties.
Watch
Why is helium used in balloons instead of hydrogen?
If a helium balloon is heated, the balloon will expand and then pop, making a loud noise. Will this also happen with a hydrogen balloon? Watch the video "Exploding Hydrogen Balloons".
If a helium balloon is heated, the balloon will expand and then pop, making a loud noise. Will this also happen with a hydrogen balloon? Watch the video "Exploding Hydrogen Balloons".
Chemical reactions do not
happen only in the laboratory. Chemical reactions happen anywhere new
substances are made. Chemical reactions occur when...
burning a candle.
cooking breakfast.
food spoils on the counter.
iron nails rust in a board.
Burning a candle is an example of a chemical reaction that produces heat. Certain types of reactions will not occur unless heat is added. A heat source, such as a stove burner, must be used to cook an egg. A chemical reaction occurs when
two or more substances combine to form new substances.
In lesson 2, you learned about exothermic and endothermic phases changes. In this section, you will learn about exothermic and endothermic reactions. An exothermic reaction is a reaction that releases energy to its surroundings. The temperature
will rise because the air around the reaction becomes warmer. Heat is always produced in an exothermic reaction.
When a log reacts with oxygen, carbon dioxide, water, and heat are produced. This is an exothermic reaction
When a log reacts with oxygen, carbon dioxide, water, and heat are produced. This is an exothermic reaction
The chemical reaction for a log burning is:
log + oxygen → ashes + carbon dioxide + water + heat
log + oxygen → ashes + carbon dioxide + water + heat
Watch
Watch "Exothermic Reactions" to confirm your knowledge on this topic.
Examples of exothermic reactions are
- fireworks exploding
- decomposition of vegetable matter (composting)
- rusting
- cellular respiration
Watch "Endothermic Reactions" to ensure that you understand this topic thoroughly.
An endothermic reaction absorbs energy from its surroundings (the air around the reaction becomes cooler).
Examples of endothermic reactions are
Examples of endothermic reactions are
- baking bread
- cooking a pancake
- producing sugar (glucose) by photosynthesis
What are word equations?
Word equations describe chemical reactions. Word equations have two parts: the reactants and the products.
Reactants: starting materials of a chemical reaction
Products: substances that are produced in a chemical reaction
Word equations describe chemical reactions. Word equations have two parts: the reactants and the products.
Reactants: starting materials of a chemical reaction
Products: substances that are produced in a chemical reaction
- Word equations use plus signs “+” to separate each element or compound. When we read a word equation, the symbol “+” stands for the word “and”.
- An arrow “→” is used to separate the reactants from the products in a chemical reaction. The “→” symbol stands for the word “produces”
- The reactants are always written on the left-hand side of the arrow.
- The products are always written on the right-hand side of the arrow
Example 1
Hydrochloric acid reacts with sodium hydroxide to produce water and sodium chloride. Write the word equation.
reactants products
hydrochloric acid + sodium hydroxide → water + sodium chloride
hydrochloric acid + sodium hydroxide → water + sodium chloride
You would read this word equation as:
"Hydrochloric acid and sodium hydroxide produce water and sodium chloride."
or
"Hydrochloric acid reacts with sodium hydroxide to produce water and sodium chloride."
"Hydrochloric acid and sodium hydroxide produce water and sodium chloride."
or
"Hydrochloric acid reacts with sodium hydroxide to produce water and sodium chloride."
Example 2
Iron metal and potassium chloride form when potassium metal reacts with iron(II) chloride. Write the word equation.
reactants products
potassium + iron(II) chloride → iron + potassium chloride
potassium + iron(II) chloride → iron + potassium chloride
You would read this word equation as:
"Potassium and iron (two) chloride produce iron and potassium chloride."
or
"Potassium chloride reacts with iron (two) chloride to produce iron and potassium chloride."
"Potassium and iron (two) chloride produce iron and potassium chloride."
or
"Potassium chloride reacts with iron (two) chloride to produce iron and potassium chloride."
Chemical Reactions Involving Oxygen
When you leave a cut apple on the table, the cut part of the apple turns brown. The enzymes in fruit react with oxygen molecules, but this brown "rusting" of fruit is considered harmless.
Oxygen is a very important reactant for many reactions. Three common chemical reactions involving oxygen are:
Oxygen is a very important reactant for many reactions. Three common chemical reactions involving oxygen are:
- corrosion
- cellular respiration
- combustion (burning)
Corrosion is a slow exothermic reaction that occurs when oxygen in the air reacts with a metal.
When iron is exposed to oxygen in the air, it corrodes and becomes iron(III) oxide.
The chemical reaction for the rusting of iron is
When iron is exposed to oxygen in the air, it corrodes and becomes iron(III) oxide.
The chemical reaction for the rusting of iron is
iron + oxygen → iron(III)oxide
Cellular Respiration
Cellular respiration occurs in both plants and animals.
Glucose (food) reacts with oxygen to form carbon dioxide, water, and energy (will be called ATP in high school courses). Because cellular respiration produces energy, it is an exothermic reaction.
glucose (food) + oxygen → carbon dioxide + water
_ energy
C6H12O6 + 9O2 → 6CO2 + 6H2O + energy
C6H12O6 + 9O2 → 6CO2 + 6H2O + energy
Figure 1 – Plant and animal cells contain thousands of mitochondria which convert sugars to energy by cellular respiration.
Combustion
Combustion is a type of exothermic reaction that occurs when a substance burns in the presence of oxygen. When a natural gas reacts with oxygen, carbon dioxide, water and heat are produced.
The chemical reaction for a natural gas burning is:
Combustion is a type of exothermic reaction that occurs when a substance burns in the presence of oxygen. When a natural gas reacts with oxygen, carbon dioxide, water and heat are produced.
The chemical reaction for a natural gas burning is:
natural gas + oxygen → carbon dioxide + water + heat
CH4 + 2O2 → CO2 + 2H2O + heat
CH4 + 2O2 → CO2 + 2H2O + heat
Water is formed by the combustion (burning) of hydrogen in this reaction.
| hydrogen | + |
oxygen
|
→ | water |
| 2H2 |
+
|
O2
|
→
|
2H2O |
|
|
|
Watch
Watch the following videos to learn more about chemical reactions.
Chemical Reactions
Chemical Reactions Involving Oxygen
Interactive
Did you notice the numbers that appeared before some of the chenical formulas in the reactions above? These are called balanced equations. the same number of atoms of each element appear before and after the reaction occurs. For example:
If you would like a "sneak peak" into balancing chemical equations, including combustion reactions, click here to visit the BrainPOP video "Chemical Equations". You will learn how to balance chemical reactions in Science 10.
You will need a username and password to access the video:
C6H12O6 + 9O2 → 6CO2 + 6H2O
If you would like a "sneak peak" into balancing chemical equations, including combustion reactions, click here to visit the BrainPOP video "Chemical Equations". You will learn how to balance chemical reactions in Science 10.
You will need a username and password to access the video:
- Username: 0099
- Password: students