Name: _______________
Skill Practice:
Interpreting a Balanced Chemical Equation
In a chemical equation, the coefficients tell us how many molecules are reacting.
Example:
1H2
+
1 molecule
1Cl2
→
1 molecule
2 HCl
2 molecules
We can represent what is happening with a diagram:
Notice that 1 hydrogen molecule and 1 hydrogen molecule make 2 hydrogen chlorides.
N2
Complete the blanks:
+
____ molecule(s)
3 H2
→
2 NH3
____ molecule(s)
____molecule(s)
1. Draw a diagram like the example above that represents what is happening in this
reaction:
A balanced equation is like a recipe. You can double or triple the recipe if you like.
Notice that any change in one coefficient will mean the other coefficients change in the
same ratio!
2 H2
+
__4___ molecule(s)
→
O2
__2__ molecule(s)
2 H2O
__4__ molecule(s)
Complete the blanks:
H2
2.
+
__3__ molecule(s)
Cl2
→
_____ molecule(s)
2 HCl
_____ molecule(s)
Since Avogadro’s number = 6.02×1023 molecules = 1 mole
2 H2
3.
+
__2__ mole
→
O2
____ mole
2 H2O
____ mole
The coefficients in a chemical equation give the mole relationships of reactants and
products in a reaction.
Give the mole relationships for each of the following:
H2
4.
____ mole(s)
C3H8
5.
Cl2 →
+
2 HCl
____ mole(s)
+
____ mole(s)
→
5 O2
____ mole(s)
____ mole(s)
3 CO2
+
____ mole(s)
4 H2O
____ mole(s)
Mole Ratios:
2 H2
+
O2
→
2 H2O
A mole ratio is the mole relationship between two specific chemicals:
Example:
 The mole ratio between H2/H2O is: 2 mole H2 = 2 mole H2O
 The mole ratio between H2/O2 is: 2 mole H2 = 1 mole O2
 The mole ratio between O2/H2O is: 1 mole O2 = 2 mole H2O
6. Using the reaction in problem 5 above:
 What is the mole ratio for C3H8/O2? ____________ = ____________
 What is the mole ratio for CO2/H2O? ____________ = ____________
 What is the mole ratio for H2O/O2? ____________ = ____________
2 Mg
+
O2 
2 MgO
7. How many moles of O2 are needed to completely react with 6 moles of Mg? Answer:
________
8. How many moles of MgO form when 3 moles of O2 react? Answer: _____
9. How many moles of O2 are required to produce 20 moles of MgO?
Answer: ________