This should be the case only when there are equal numbers of moles on the right and left in the balanced equation. Use the van't Hoff equation. Answers are in the back of the book for this one. This is like Problem 3, except that you have the pressures and are working backwards. No equilibrium constant is given, and it is not certain whether after another 50 seconds the pressures of the two gases will remain constant.
More experimental data is needed.
No, it is endothermic. The equilibrium shifts to the right when the temperature is raised. See me if you don't know how to do this. See me if you cannot do this. The number of moles of OH - therefore is 0.52 moles.