Calculating Reaction Rates

Question

In a combustion experiment, 9 moles of methane gas reacts completely in a 3 L container containing excess oxygen gas in 3.5 s. Express the average rate of production of carbon dioxide gas in units of M/s

Answer 1

Look at the balanced equation.

CH4 + 2O2 ==> CO2 + 2H2O

9 moles CH4/3.5 sec produces 9 moles CO2/3.5 sec because the mole ratio is 1:1 for CH4 : CO2

On a molar basis, this is 9 mole/3L = 3 M

Thus the answer would be 3 M/3.5 s = 0.857 M/s = 0.9 M/s to 1 significant figure.