Using the Equilibrium Constant The reversible chemical reaction A+B?C+D has the

Question

Using the Equilibrium Constant

The reversible chemical reaction

A+B?C+D

has the following equilibrium constant: Kc=[C][D][A][B]=3.0

Part A

Initially, only A and B are present, each at 2.00 M. What is the final concentration of A once equilibrium is reached?

Express your answer to two significant figures and include the appropriate units.

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Part B

What is the final concentration of D at equilibrium if the initial concentrations are [A] = 1.00M and [B] = 2.00M ?

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

Kc = [C] [D] / [A][B]

Initially [A] = [B] = 2 and [c]= [D] = 0

let at equilbirium

[A] = [B] = 2-x

[C] = [D] = x

3 = x^2 / (2-x)^2

3 [4 + x^2 - 4x ] = x^2

12 + 3x^2 - 12x = x^2

2x^2 + 12 -12x = 0

on solving

x = 4.73 ( not possible )

x = 1.26M = [C]

so [A] = 2-1.26 = 0.74

2.

3 = x^2 / (2-x) (1-x)

3 [2 + x^2 - 3x ] = x^2

6 + 3x^2 - 9x = x^2

2x^2 + 6 -9x = 0

on solving

x = 3.8 ( not possible )

x = 0.81M = [C] = [D]

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