Pressure!!! -Chemistry?

Question

Gaseous hydrogen and oxegen reacts in closed vessel at 20degrees to form water:
H2 + 1/2 O2 = H20

What would graph of pressure within vessel as time passes be like??
If vessel contains 0.2 mol oxygen and 1 mol hydrogen determine initial and final pressure

Answer 1

Forming water which is liquid at 20C diminishes the pressure since the amount of gas decreases. So you have a decreasing curve until all oxygen has been used .
You see with the formula that you need 1 mole of hydrogen for 0.5 mole of oxygen
So you form 0.2 mole of water using 0.2mole of xygen and 0.4 mole of hydrogen
At time zero, you had 1.2 moles of gases (1mole hydrogen+0.2 mole of oxygen). at the end you have only 0.6 mole of hydrogen left.
so the pressure will be 0.6/1.2 = 1/2
pressure is halved