Question and Inquiry

Question

4. Consider the decomposition of nitrogen trifluoride into nitrogen and fluorine below:

2 NF3  ⇆   N2(g) + 3 F2(g)  

1. When 2.06 mol of NF3 is initially placed in a 2.00 L container and allowed to come to equilibrium at 800K, the equilibrium mixture is found to contain 0.0228 mol of N2 gas. What is the equilibrium constant at this temperature?

1. After decreasing the temperature, the equilibrium constant changes to Keq = 4.5 x 10-6 the concentrations become the following:

[NF3] = 1.00 M, [F2] = 0.042 M and [N2] = 0.014 M,    

i. Determine the reaction quotient, Q

 

ii. Is the system at equilibrium? If it is not, describe how the system has to shift in order to reach equilibrium.

Answer 1

2NF₃ <==> N₂ + 3F₂

2.06...........0.........0......Initial

-2x...........+x.......+3x....Change

2.06-2x.....x........3x......Equilibrium

x = 0.0228 as given in the question.

Equilibrium concentration are as follows:

[NF3] = 2.06 - 0.0456 = 2.01 / 2 L = 1.01 M

[N2] = 0.0228 / 2 L = 0.0114 M

[F2] = 3 x 0.0228 = 0.0684 / 2L = 0.0342 M

K = [N2][F2]³ / [NF3]² = (0.0114)(0.0342)³ / (1.01)²

K = 4.47x10^-7

Q = [N2][F2]³ / [NF3]² = (0.014)(0.042)³ / (1.00)² = 1.04x10^-6

Since Q < K, the system is NOT at equilibrium. In order to reach equilibrium the system must shift to the right to make more products such that Q = K