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± Calculating Equilibrium Constants For a gaseous reaction with the general form

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Question

± Calculating Equilibrium Constants

For a gaseous reaction with the general form

aA+bBcC+dD

Kc=[C]c[D]d[A]a[B]b

Kp=(PC)c(PD)d(PA)a(PB)b

Part A

CO(g)+Cl2(g)COCl2(g)

Express your answer numerically.

.136

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Deriving concentrations from data

In Part A, you were given the equilibrium pressures, which could be plugged directly into the formula for K. In Part B however, you will be given initial concentrations and only one equilibrium concentration. You must use this data to find all three equilibrium concentrations before you can apply the formula for K.

Part B

H2(g)+I2(g)2HI(g)

Express your answer numerically.

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± Calculating Equilibrium Constants

The equilibrium constant, K, of a reaction at a particular temperature is determined by the concentrations or pressures of the reactants and products at equilibrium.

For a gaseous reaction with the general form

aA+bBcC+dD

the Kc and Kp expressions are given by

Kc=[C]c[D]d[A]a[B]b

Kp=(PC)c(PD)d(PA)a(PB)b

The subscript c or p indicates whether K is expressed in terms of concentrations or pressures. Equilibrium-constant expressions do not include a term for any pure solids or liquids that may be involved since their composition does not change throughout the reaction. The standard state of a pure substance is the pure substance itself, and although the quantity may change the sample remain pure. The concentration is effectively equal to 1, and will not impact the magnitude of K.

Part A

Phosgene (carbonyl chloride), COCl2, is an extremely toxic gas that is used in manufacturing certain dyes and plastics. Phosgene can be produced by reacting carbon monoxide and chlorine gas at high temperatures:

CO(g)+Cl2(g)COCl2(g)

Carbon monoxide and chlorine gas are allowed to react in a sealed vessel at 469 C . At equilibrium, the concentrations were measured and the following results obtained: Gas Partial Pressure
(atm) CO 0.900 Cl2 1.19 COCl2 0.280 What is the equilibrium constant, Kp, of this reaction?

Express your answer numerically.

Kp =

.136

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Incorrect; Try Again; 5 attempts remaining

Deriving concentrations from data

In Part A, you were given the equilibrium pressures, which could be plugged directly into the formula for K. In Part B however, you will be given initial concentrations and only one equilibrium concentration. You must use this data to find all three equilibrium concentrations before you can apply the formula for K.

Part B

The following reaction was performed in a sealed vessel at 713 C :

H2(g)+I2(g)2HI(g)

Initially, only H2 and I2 were present at concentrations of [H2]=4.00M and [I2]=2.05M. The equilibrium concentration of I2 is 0.0700 M . What is the equilibrium constant, Kc, for the reaction at this temperature?

Express your answer numerically.

Kc =

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Explanation / Answer

Answer –

Part A) We are given, reaction –

CO(g)+Cl2(g) ,------> COCl2(g)

At equilibrium, partial pressure is

CO = 0.900 atm , Cl2 = 1.19 atm and COCl2 = 0.280 atm

We know Kp expression for the give reaction

Kp = P(COCl2(g)) / P(CO(g))*P(Cl2(g))

      = (0.280 ) / (0.900 * 1.19)

      = 0.261

So, Kp = 0.261

Part B) We are given, reaction

H2(g)+I2(g) <-----> 2HI(g)

[H2] = 4.00 M , [I2] = 2.05 M ,

At equilibrium I2 = 0.0700 M

We need to put ICE chart

       H2(g)+I2(g) <-----> 2HI(g)

I      4.00    2.05                  0

C       -x        -x                  2x

E 4.00-x     2.05-x            +2x

So at equilibrium I2 = 2.05-x

So, 0.0700 M = 2.05-x

    x = 2.05-0.0700

        = 1.98

So at equilibrium

[H2] = 4.00-x

        = 4.00 -1.98

        = 2.02 M

[I2] = 0.0700 M

[HI] = 2x

       = 2*1.98

       = 3.96 M

So, Kc = [HI]2 / [ H2] [I2]

           = (3.96)2 / (2.02*0.0700)

           = 111

    Kc = 111