Lab #2 Resource Page
This week’s investigation will focus on the rate at which chemical reactions occur. Before you arrive you will need to
know the following:
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What is a chemical reaction?
Be able to give examples of chemical reactions.
What are the signs of a chemical reaction?
What is a reactant?
What is a product?
What are the basic rules for writing a chemical reaction?
What is a physical change?
How are physical changes different from chemical reactions?
What things can determine the rate at which a chemical reaction can take place?
A chemical reaction occurs when two or more chemicals are combined and produce a completely different substance
with new and different physical and chemical properties. Chemical reactions cannot easily be reversed. There are
several signs which indicate that a chemical reaction has occurred. These signs are as follows:
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Color change
o An example of a chemical reaction that involves color change is the changing of leaves from green to
orange or red in the fall.
Energy is absorbed
o Baking bread is an example of a chemical reaction in which energy (heat) is absorbed.
Energy is released
o The combustion of gasoline in a car is an example of a reaction in which energy is released.
Light is emitted
o Fireworks are an example of a chemical reaction in which light is emitted.
Odor change occurs
o A chemical reaction that involves an odor change occurs in rotting eggs.
Gas is produced
o Vinegar and baking soda mix to form a chemical reaction that produces carbon dioxide gas.
Solid is produced (we call this a precipitate)
o A chemical reaction between oxygen and iron forms rust, a precipitate, also known as iron oxide.
A reactant can be defined as a chemical substance that is present before a chemical reaction occurs. I call these the
‘ingredients’. They are the chemicals that when combined start a chemical reaction. Reactants are always written on
the left of the arrow.
Reactants
A product can be defined as a chemical substance that is formed after a chemical reaction occurs. This is what is made
as a result of the chemical reaction. Products are always written on the right side of the arrow.
Products
The reactants and products together are called a chemical reaction. A chemical reaction can be written in an equation
that shows the reactants, and the products yielded from the chemical reaction. A chemical reaction can be written as
follows:
Reactants
Products
We list the reactants and products with plus signs in between each. For example:
Reactant 1 + Reactant 2
Product 1 + Product 2
OR using real chemicals like this:
3HCO3 + 3H
3H2O + 3CO2
Many people often confuse chemical reactions with physical changes. Physical changes occur when a substance
changes only its physical properties. Unlike chemical reactions, physical changes can be reversed. This means that a
new product is not made. Physical changes include changes in properties such as:
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Size
Shape
State of matter (solid, liquid, or gas)
o Freezing, melting, evaporation, condensation, and sublimation are examples of physical changes
involving a change from one state of matter to another.
A classic example of a physical change is freezing water into ice cubes. Even though the water is in a different state (it’s
a solid not a liquid anymore, right?), it is still H20, the chemical water.
Chemical reactions can occur at different rates. For example, a firework’s reaction happens quickly while bread baking is
a much slower reactions. The following are items which may influence the rate at which a chemical reaction occurs:
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The concentrations of reactants present.
The surface area of the two reactants
The pressure at which the reaction is taking place.
The amount of energy required to make the reaction start and carry on may be different for different
substances.
5. The temperature at which the reaction is taking place.
6. The presence or absence of a catalyst.