1. 1
14. Representing chemical change
Chemistry: Chemical change
Grade 10
Everything Science www.everythingscience.co.za

2. 2
Chemical equations
A chemical equation uses symbols to describe a chemical reaction.
In a chemical equation, reactants are written on the left hand side of the equation and the
products on the right. The arrow is used to show the direction of the reaction.
When representing chemical change, it is important to be able to write the chemical formula
of a compound.
Chemical equations allow us to concisely show what happens in a reaction:
Sentence: Iron reacts with sulphur to form iron sulphide
Word equation: Iron + sulphur → iron sulphide
Chemical equation:
FeS FeS
Everything Science www.everythingscience.co.za

3. 3
Conservation of mass
The law of conservation of mass states that the mass of a closed system of substances will
remain constant, regardless of the processes acting inside the system. Matter can change
form, but cannot be created or destroyed.
In any chemical reaction, the law of conservation of mass applies. This means that the total
atomic mass of the reactants must be the same as the total atomic mass of the products.
This also means that the total number of atoms of the reactants must be the same as the
total number of atoms of the product.
Everything Science www.everythingscience.co.za

4. 4
Balancing chemical equations
If the number of atoms of each element in the reactants is the same as the number of atoms of
each element in the product, then the equation is balanced.
The equation below is not balanced. To balance it the co-efficients of the molecules need
to be changed.
Everything Science www.everythingscience.co.za

5. 5
Balancing chemical equations continued
Once a chemical equation is balanced we can add state symbols to the equation. We use g for
gas, l for liquid, s for solid and aq for aqueous.
Using the example on the previous slide we get:
CH (g)2 O (g)  CO 2 (g)2 H 2 O (l)
4 2
We can use this equation in chemical calculations.
Everything Science www.everythingscience.co.za

6. 6
For more practice or to ask an expert for help on this
section see:
www.everythingscience.co.za
ESADY
Everything Science www.everythingscience.co.za