I've never done a reaction that involved just bond enthalpies before, so this is just a guess.
It's still products - reactants. The problem is the C=O bond. Do you count it once or twice? I'm going to choose once, but don't be surprised if it is incorrect.
Sum of the products - Sum of the reactants.
ΔH = 799 - 494
ΔH = 305
And that would be your answer to three places.
According to Gayle Lusac's law, pressure is proportional to absolute temperature of a gas. Thus:
P/T = constant
So if the temperature becomes 3T, the pressure would increase to 3P
