What volume of hydrogen is required to react with 12 L of oxygen under the same conditions?2H2(g) + O2(g) ? 2H2O(g).

Question

What volume of hydrogen is required to react with 12 L of oxygen under the same conditions?2H2(g) + O2(g) → 2H2O(g).

Answer 1

Assume that all gases are ideal and that reaction occurs at STP (not necessary, but makes the problem more familiar):

12L of oxygen:

                          n_O = (1atm)*(12L)/((0.082atm L/mol K)(298K)) = 0.491mol

For complete reaction, need 2 moles of H₂ for each mole of O₂.

                          n_H = 0.982mol

To find volume, use the ideal gas equation:

                          V_H = (0.982mol)*(0.082atm L/mol K)*(298K)/(1atm) = 24L

Note, this is just double the volume of oxygen. This works since, assuming constant temp and pressure throughout reaction:

                                                n_O/n_H = V_O/V_H