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 (sum moles products - sum moles reactants). For example, consider the reaction

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

for which

Part A

For the reaction

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

Kc = 34.2 at a temperature of 183 ?C .

Calculate the value of Kp.

Express your answer numerically.

?n=2?(1+3)=?2

Part B

For the reaction

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

Kp = 2.82×10?2 at a temperature of 19 ?C .

Calculate the value of Kc.

Express your answer numerically.

Explanation / Answer

A)

T= 183.0 oC

= (183.0+273) K

= 456 K

? n = number of gaseous molecule in product - number of gaseous molecule in reactant

? n = -4

use:

Kp= Kc (RT)^? n

Kp = 34.2*(0.08206*456.0)^(-4)

Kp = 1.744*10^-5

Answer: 1.74*10^-5

B)

T= 19.0 oC

= (19.0+273) K

= 292 K

? n = number of gaseous molecule in product - number of gaseous molecule in reactant

? n = -1

use:

Kp= Kc (RT)^?n

0.0282 = Kc *(0.08206*292.0)^(-1)

Kc = 0.676

Answer: 0.676

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