7.1 Describing Reactions
Reading Focus
Key Concepts
What is the law of conservation of mass?- Why must chemical equations be balanced?
- Why do chemists use the mole?
- How can you calculate the mass of a reactant or product in a chemical reaction?
Vocabulary
reactants
products
chemical equation
coefficients
mole
molar mass
Reading Strategy
Monitoring Your Understanding Preview the Key Concepts, topic headings, vocabulary, and figures in this section. List two things you expect to learn. After reading, state what you learned about each item you listed.
What I Expect to Learn |
What I Learned |
|---|---|
a.____?______ |
b.____?______ |
c.____?______ |
d.____?______ |
Figure 1 Burning is an example of a chemical reaction. When charcoal burns, the carbon in the charcoal reacts with oxygen in the air to produce carbon dioxide and heat.
What type of change is happening in Figure 1? When charcoal burns, it changes into other substances while producing heat and light. Burning is a chemical change. When a substance undergoes a chemical change, a chemical reaction is said to take place. In order to understand chemical reactions, you first must be able to describe them.
Chemical Equations
A useful way of describing a change is to state what is present before and after the change. For example, suppose you wanted to show how your appearance changed as you grew older. You could compare a photo of yourself when you were younger with a photo that was taken recently.
A useful description of a chemical reaction tells you the substances present before and after the reaction. In a chemical reaction, the substances that undergo change are called reactants. The new substances formed as a result of that change are called products. In Figure 1, the reactants are the carbon in the charcoal and the oxygen in the air. The product of the reaction is carbon dioxide gas.
Using Equations to Represent Reactions
During a chemical reaction, the reactants change into products. You can summarize this process with a word equation.
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