Question

Consider the reaction shown below.

PbCO3(s) PbO(s) + CO2(g)

Calculate the equilibrium pressure of CO2 in the system at the following temperatures.

(a) 240°C

? atm

(b) 600°C

? atm

Note: To find the value of the equilibrium constant at each temperature you must first find the value of G0 at each temperature by using the equation G0 = H0 - TS0 For this reaction the values are H0 = +88.3 kJ/mol and S0= 151.3 J/mol*K

Answer 1

(a) 240°C = 513 K

Equilibrium constant K = P_CO2 = equilibrium pressure of CO₂

ΔG^o = ΔH^o - TΔS^o

ΔG^o = 88.3 x 10³ - 513 x 151.3

ΔG^o = 10683.1 J/mole

ΔG^o = -RT ln K

10683.1 = -8.314 x 513 x ln K

K = 0.08169

Equilibrium pressure of CO₂ = 0.08169 atm

(b) 600°C = 873 K

Equilibrium constant K = P_CO2 = equilibrium pressure of CO₂

ΔG^o = ΔH^o - TΔS^o

ΔG^o = 88.3 x 10³ - 873 x 151.3

ΔG^o = -43784.9 J/mole

ΔG^o = -RT ln K

-43784.9 = -8.314 x 873 x ln K

K = 416.7716

Equilibrium pressure of CO₂ = 416.7716 atm