Chemical Reactions
A chemical reaction occurs when substances (reactants) are transformed into new substances (products) with different properties. Evidence of a reaction includes colour change, gas production, or temperature change.
What You Need to Know
Key Concept Diagram
Reactants are the starting substances; products are the new substances formed in a reaction
Signs of a chemical reaction: colour change, bubbling/gas production, temperature change, light emission, or new smell
Burning (combustion), rusting (oxidation), cooking, and digestion are all chemical reactions
Chemical changes are usually irreversible — the products cannot easily be changed back into the reactants
Key Vocabulary
Reactant
A substance that takes part in and is changed by a chemical reaction
Product
A new substance formed as a result of a chemical reaction
Combustion
A chemical reaction between a fuel and oxygen that releases heat and light (burning)
Oxidation
A chemical reaction in which a substance combines with oxygen, e.g. rusting
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
Which observation is the BEST evidence that a chemical reaction has occurred?
Question 2
When wood burns, what type of reaction is occurring?
Question 3
Rusting is an example of which type of chemical reaction?
Key Concepts Summary
- ●Reactants are the starting substances; products are the new substances formed in a reaction
- ●Signs of a chemical reaction: colour change, bubbling/gas production, temperature change, light emission, or new smell
- ●Burning (combustion), rusting (oxidation), cooking, and digestion are all chemical reactions
- ●Chemical changes are usually irreversible — the products cannot easily be changed back into the reactants