I'm not sure even where to start on this problem:
given the equation 2NaHCO3 (s) <---------> Na2CO3 (s) + H2O (g) + CO2 (g)
A sample of 100. grams of solid NaHCO3 was placed in a previously evacuated rigid 5.00 liter container and heated to 160 degrees C. Some of the original solid remained and the total pressure in the container was 7.76 atmospheres when equilibrium was reached. Calculate the number of moles of H20 (g) present at equilibrium.
I tried using Kp and partial pressures but I haven't done enough of these kind of problems to know what to do. Thanks in advance!