7.1 Describing Chemical Reactions
A chemical reaction has occurred if the product(s) is chemically different to the reactants
1. What is meant by the terms:
The reactant(s) will change into the product(s) in a chemical reaction.
2. In the diagram below,
a. What is the reactant(s)?
b. What is the product(s)?
How to set out a chemical equation
Chemical equations are written so that the reactants are shown first and are separated by a plus sign (+). The reaction itself is represented by an arrow that points to the products of the reaction. The products are also separated by plus signs. For example, when we add magnesium metal to hydrochloric acid, the new substances magnesium chloride and hydrogen gas are formed.
3. Use the following words to write a basic chemical equation
· Reactant 2
· Product 1
· Reactant 1
· Product 2
The Law of Conservation of Mass
In the eighteenth century, Antoine-Laurent Lavoisier provided the evidence on which these ideas are based. He showed that although a candle seems to disappear as it burns, there is as much mass present after it has completely burnt as there was before.
The loss of mass was caused by gases moving into the atmosphere. Lavoisier's ideas led to the development of the Law of Conservation of Mass.
4. Write a definition for the Law of Conservation of Mass (p 226)
Lavoisier also provided evidence for the Law of Constant Proportions.
5. Write a definition for the Law of Constant Proportions (p 226)
For example, carbon dioxide (CO2) always contains the same relative amounts of carbon and oxygen (about 27 per cent of the mass is made up of carbon). It does not matter whether the carbon dioxide forms from the reaction of sherbet in your mouth, or from the reaction in the engine of a motorcycle, this proportion is fixed...