chemistry -- partial pressure?

Question

I'm stuck on this problem in chem,, I balanced the equation but am not too sure as to what I'm supposed to do now. Here's the problem and equation:

Methane is burnt in oxygen to produce carbon dioxide and water vapor. The final pressure of the gaseous products was 6.25 torr. Calculate the partial pressure of the water vapor.

CH4 + 202 --(heat)--> CO2 + 2H20

...now what? Can anyone help?!?

Answer 1

Think of the ideal gas law PV = nRT.

In the above reaction both gases occupy the same volume and the same temperature. So those variable drop out. All that's left is that the pressure of each is proportional to the moles of each. Your equation shows 1 mole of CO2 and 2 moles of water.

I would conclude that the partial pressure of each is 1/3 of the total for CO2 and 2/3 for water.