The equilibrium constant, K c, is calculated using molar concentrations. For gas

Question

The equilibrium constant, Kc, is calculated using molar concentrations. For gaseous reactions another form of the equilibrium constant, Kp, is calculated from partial pressures instead of concentrations. These two equilibrium constants are related by the equation

Kp=Kc(RT)n

where R=0.08206 Latm/(Kmol), T is the absolute temperature, and n is the change in the number of moles of gas (sum moles products - sum moles reactants). For example, consider the reaction

N2(g)+3H2(g)2NH3(g)

for which n=2(1+3)=2.

_____________________________________________

Question # 1 :

For the reaction

2A(g)+3B(g)C(g)

Kc = 70.6 at a temperature of 121 C .

Calculate the value of Kp.

Question # 2

For the reaction

X(g)+3Y(g)3Z(g)

Kp = 2.84×102 at a temperature of 279 C .

Calculate the value of Kc.

Explanation / Answer

2A(g)+3B(g)C(g)    Kc = 70.6

Kp=Kc(RT)^n

Kp = 70.6 (0.0821 * 394)^ (1-5)

Kp = 6.448 *10^-5

X(g)+3Y(g)3Z(g)

Kc = (2.84 *10^-2 ) / (0.0821 * 552)^(3-4)

Kc = 1.287

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