A 0.831 gram sample of SO 3 is placed in a 1.00 L rigid container and heated to

Question

A 0.831 gram sample of SO3 is placed in a 1.00 L rigid container and heated to 1100 K. The SO3 decomposes to SO2 and O2 :

                                    2SO3(g) 2SO2(g) + O2(g)

At equilibrium, the total pressure in the container is 1.300 atm. Calculate the value of Kp at 1100 K

Extra Credit: Consider two containers A and B where A is a rigid container and B is a container with a massless, frictionless piston that maintains constant pressure. NH3(g) is injected into both containers and allowed to come to equilibrium. At equilibrium, 2 atm of Argon gas is injected into each container. Explain any changes (up, down or no change) to the equilibrium concentrations of NH3, N2and H2?

Explanation / Answer

A 0.831 gram sample of SO3 is placed in a 1.00 L rigid container and heated to 1100 K. The SO3 decomposes to SO2 and O2 :

                                    2SO3(g) 2SO2(g) + O2(g)

At equilibrium, the total pressure in the container is 1.300 atm. Calculate the value of Kp at 1100 K

Solution :- lets first calculate the moles of SO3

Moles of SO3 = 0.831 g / 80.0632 g per mol = 0.010379 mol SO3

Now lets calculate the initial pressure of the SO3

PV= nRT

P= nRT/V

= 0.010379 mol * 0.08206 L etm per mol K * 1100 K /1.0 L

= 0.9369 atm

2SO3   ----- > 2SO2    + O2

0.9369 atm      0             0

-2x                    +2x       +x

0.9369-2x           2x           x

At equilibrium total repssure is 1.30 atm

Value of x = 1.30 atm – 0.9369 atm

                = 0.3631 atm

So the equilibrium pressures are as follows

SO3 = 0.9369 atm – 2x = 0.9369 atm – (2*0.3631 atm) = 0.211 atm

SO2 = 2x = 2*0.3631 atm = 0.7262 atm

O2 = 0.3631 atm

Now lets calculate the equilibrium constant

K = [SO2]^2[O2]/[SO3]^3

    =[0.7262]^2[0.3631]/[0.211]^2

    = 4.30

Extra Credit: Consider two containers A and B where A is a rigid container and B is a container with a massless, frictionless piston that maintains constant pressure. NH3 (g) is injected into both containers and allowed to come to equilibrium. At equilibrium, 2 atm of Argon gas is injected into each container. Explain any changes (up, down or no change) to the equilibrium concentrations of NH3 , N2 and H2 ?

Solution :- The container A which is rigid container when Ar is added to it then it increases the pressure in the container which causes the left shif in the equilibrium therefore the concentration of the NH3 will increase and concentration of the N2 and H2 will decrease.

The container with moving piston will reequilibrate and the concentrations of the NH3 and N2 and H2 will not change.

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