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Lesson 3.1
List three things you have learned about chemical reactions.
Chemical reactions can be simple (combustion of hydrogen fuel) or complex (taking an antacid).
Chemical changes can be obvious (a candle burning) or less noticeable (reactions that make a cake rise or iron rust).
Chemical reactions can occur immediately (explosions) or slowly (ripening of a banana).
Why do chemists use word equations to represent chemical reactions?
Chemists use word equations to represent chemical reactions because it is a convenient way to show which chemicals went into the reaction and which chemicals were produced.
Describe the standard format for writing word equations for a chemical reaction.
The left side of the equation lists all the reactants.
The right side of the equation lists all the products.
An arrow points from the reactants to the products. It shows that something is produced during the chemical reaction.
What is the purpose of the plus (+) in a word equation that represents a chemical reaction?
The purpose of the plus sign ( +) is to separate the reactants and products when there are more than one of each.
Lesson 3.2 and 3.3
List two reasons why chemists use patterns to group reaction types.
Chemists use patterns to group reaction types because it allows them to predict the product of an unknown reaction. It also helps them understand the behaviour of substances in a chemical reaction.
a) Write the word equation for the reaction of magnesium and oxygen.
Magnesium + oxygen → magnesium oxide + light + thermal energy (heat)
b) Name the reactants and products in this reaction.
The reactants are magnesium and oxygen. The product is magnesium oxide. Light and thermal energy are not called products.
c) How many elements are used as reactants?
Two elements are used as reactants
d) What happens to the reactants during this reaction?
The reactants combine to form a compound called magnesium oxide.
Describe, in words, the general form of a simple composition reaction.
In a simple composition reaction, two or more elements combine to form a compound.
Write the general form of a simple composition reaction using the letters A and B.
A + B → AB
Are most simple composition reactions exothermic or endothermic?
Most simple composition reactions are exothermic.
Why is it important to know if a reaction is exothermic or endothermic?
It is important to know if a reaction is exothermic or endothermic because exothermic reactions release energy. If the amount of energy released is large enough, it can be dangerous to the person conducting the reaction.
Another type of chemical reaction is the simple decomposition reaction. In simple decomposition reactions, a compound is separated into its elements. Read the information on Simple Decomposition Reactions (page 45) and respond to the following questions.
a) Write a word equation for the electrolysis of water.
Water + electric energy → hydrogen gas + oxygen gas
b) What is the reactant in this reaction? What is the product?
The reactant is water. The products are hydrogen gas and oxygen gas.
In a simple decomposition reaction, the products are always _______________________.
elements
Write the general form for a simple decomposition reaction using the letters C and D.
CD → C + D
Most decomposition reactions are endothermic. What does this mean in terms of energy for these reactions?
This means the simple decomposition reactions require energy to drive the reaction.
Describe how simple composition reactions compare to simple decomposition reactions.
Simple composition reactions are opposite to simple decomposition reactions.
In a simple composition reaction, elements are combined to form a compound.
In a simple decomposition reaction, a compound is broken apart into its elements.
Most simple composition reactions release energy, whereas most simple decomposition reactions require energy.
Read “Did you Know?” on page 45. How do chemists today protect themselves from the hazards that past experimenters, like Sir Humphry Davy, experienced?
Chemists, today , have an extensive knowledge of reaction types and are able to predict the products of the reactions. They also have sophisticated laboratory equipment that protects them from the products of reactions. They also know the dangers of coming in contact with hazardous chemicals.
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