Question

NO reacts with Cl2 to form NOCl. The equilibrium constant, Kp, for this reaction is 5.56 at 573 K.

2NO(g) + Cl2(g) 2NOCl(g)

The standard enthalpy change for this reaction (ΔH°) is -77.1 kJ/mol.

(a) Predict the effect on the production of NOCl when the temperature of the equilibrium system is decreased.

*production is favored or production is disfavored

(b) Use the van’t Hoff equation to estimate the equilibrium constant for this reaction at 488 K.

Kp at 488 K =

Answer 1

(a) According to LeChatellier's principle, increasing the temperature of an exothermic reaction would disfavor the formation of product. Thus in the given reaction being an exothermic reaction, the equilibrium will shift towards the reactant side upon increasing the equilibrium temperature..

(b) Van't hoff equation,

ln(Kp2/Kp1) = dH/R[1/T1 - 1/T2]

with,

Kp1 = 5.56

T1 = 573 K

Kp2 = ?

T2 = 488 K

dH = -77.1 kJ/mol

R = gas constant

we get,

ln(Kp2/5.56) = -77100/8.314 [1/573 - 1/488]

Kp2 = 93.182

So the equilibrum constant for this reaction at 488 K, would be Kp = 93.182