Page 89 - Chemistry_Form_2

Chemistry
for Secondary Schools

Step 2: Write the unbalanced chemical equation using symbols
The reactants are zinc (Zn) and hydrochloric acid (HCl), and the products are
zinc chloride (ZnCl ) and hydrogen gas (H ):
2 2

2 FOR ONLINE READING ONLY
Step 3: List the number of atoms on both sides
Reactants (left side):
Zn: 1 zinc atom

HCl: 1 hydrogen atom and 1 chlorine atom per molecule
Products (right side):
ZnCl : 1 zinc atom and 2 chlorine atoms
2
H : 2 hydrogen atoms
2
There are two chlorine atoms in ZnCl but only one chlorine atom from HCl on
2
the left. Also, there are two hydrogen atoms in H but only one hydrogen atom
2
from HCl on the left.

Step 4: Balance the equation

To balance the equation, two HCl molecules are required to produce two chlorine
atoms and two hydrogen atoms:

Step 5: Verify the balancing

Count atoms of all the elements on both sides to make sure they are equal.
Reactants (left side):
Zn: 1 zinc atom

2HCl: 2 hydrogen atoms and 2 chlorine atoms
Products (right side):

ZnCl : 1 zinc atom and 2 chlorine atoms
2
H : 2 hydrogen atoms
Since the number of the atoms is equal on both sides, the equation is balanced.

Step 6: Write the balanced chemical equation with its state symbols

82 Student’s Book Form Two

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