Find Kp given Total Pressure?

Question

A sample of solid ammonium chloride was placed in an evacuated container and then heated so that it decomposed to ammonia gas and hydrogen chloride gas. After heating, the total pressure in the container was found to be 4.4 atm. Calculate Kp at this temperature for the following decomposition reaction.

NH4Cl(s) <--> NH3(g) + HCl(g)

Answer 1

From your equation, you can see that the moles of NH3 must equal the moles of HCl. So, the pressures of the two gases are equal and must add together to be 4.4 atm. So, the pressure of each gas is 2.2 atm.

For this equation Kp=P(NH3) X P(HCl) = 2.2 X 2.2 = 4.8 atm^2