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 L?atm/(K?mol), T is the absolute temperature, and ?n is the change in the number of moles of gas. For example, consider the reaction

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

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

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Part A

For the reaction

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

Kc = 97.4 at a temperature of 269?C .

Calculate the value of Kp.

Express your answer numerically.

Kp = ?

Part B

For the reaction

X(g)+3Y(g)?2Z(g)

Kp = 3.45

Kp = ?

Part B

For the reaction

X(g)+3Y(g)?2Z(g)

Kp = 3.45

Explanation / Answer

(A) 2 A + 3 B <=> C

Change in moles of gas Dn = 1 - 2 - 3 = -4

T = 269 deg C = 542.15 K

R = 0.08206 atm.L/mol.K

Kp = Kc x (RT)^(Dn)

= 97.4 x (0.08206 x 542.15)^(-4)

= 2.49 x 10^(-5) = 2.49 x 10-5

(B) X + 3 Y <=> 2 Z

Change in moles of gas Dn = 2 - 1 - 3 = -2

T = 15 deg C = 288.15 K

R = 0.08206 atm.L/mol.K

Kc = Kp x (RT)^(-Dn)

= 3.45 x 10^(-2) x (0.08206 x 288.15)^(2)

= 19.3

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