How to do this chemistry problem with gases?

Need Help With a Chemistry problem containing gases and pressure!!?

• A 40.0 L stainless steel container was charged with 5.00 atm of hydrogen gas and 6.00 atm of oxygen gas. A spark ignited the mixture, producing water. What is the pressure in the tank at a constant temperature of 25°C? i wrote the equation 2 H2(g) + O2(g) -> 2 H2O(g) and got 8.18 mol of H2 and got 9.81 mol of O2 and then have no idea what to do? and how do i do: a) If the open-tube manometer in the figure below contains a nonvolatile silicone oil (density = 1.30 g/cm3) instead of mercury (density = 13.6 g/cm3), what are the pressures in the flask as shown in parts a and b in torr, atmospheres, and pascals? (The atmospheric pressure above the tubes is 760. torr.)

• Answer:

  You now need to determine which gas is the limiting reagent. From this you can find out how much gas is left from the other reagent, and calculate the pressure from the number of moles of remaining gas. I calculate it to be between 3 and 4 atm. You would take the height of the silicone oil and multiply it by the density of the oil and the gravitational constant (in cm/s2). This will give us a pressure (dyne/cm2) in addition to the 1 atm (1013300 dyne/cm2) that is pushing down on the end of the oil. It is then a matter of converting the pressure to the correct units.