Answer:
32 moles of Oxygen
Step-by-step explanation:
C3H8 + O2 --> CO2 + H2O
There are 3 Cs on the left so you need to make 3 Cs on the right
C3H8 + O2 --> 3 CO2 + H2O
There are 8 Hs so you need to make 8 Hs on the right
4 times H2 makes 8 so put a 4 in front of H2
C3H8 + O2 --> 3 CO2 + 4 H2O
Then find the number of oxygen on the right
3 times O2 + 4 times O
6 + 4 = 10 Os
So put 5 in front of O2 to make 10
because 5 times 2 is 10
C3H8 + 5 O2 --> 3 CO2 + 4 H2O
Now it is balanced
and you can check
Left: C= 3 H= 8 O= 10
Right: C= 3 H= 8 O= 6+4
Now you need to find how many moles of oxygen are necessary to react to 4 moles of C3H8
4 moles of C3H8 is just 4 C3H8
Just multiply the whole equation by 4
4 C3H8 + 20 O2 --> 12 CO2 + 16 H2O
C = 12 H = 32 O = 40
C = 12 H = 32 O = 24 + 16 which is 40
When a number is in front you multiply each element with it
12 times 2Os = 24 16 times 1 O
So 32 moles are necessary to react to 4 moles of C3H8