Question

Consider the reaction between NO and Cl2 to form NOCl:

2NO(g) + Cl2(g) ⇌ 2NOCl(g)
A reaction mixture at a certain temperature initially contains only [NO]= 0.61 M and [Cl2] = 0.57 M. After the reaction comes to equilibrium, the concentration of NOCl is 0.36 M.
Find the value of the equilibrium constant (Kc) at this temperature.
a) 3.16
b) 1.58
c) 0.79
d) 0.40
e) none of these

Answer 1

The equilibrium constant (Kc) for the reaction 2NO(g) + Cl2(g) ⇌ 2NOCl(g) is calculated using the equilibrium concentrations of the reactants and products. After appropriate calculations, the closest value from the options provided is 1.58.

Step-by-step explanation:

To determine the equilibrium constant (Kc) for the reaction 2NO(g) + Cl2(g) ⇌ 2NOCl(g), given that the equilibrium concentration of NOCl is 0.36 M, we need to calculate the changes in concentration of NO and Cl2. Initially, [NO] was 0.61 M and [Cl2] was 0.57 M. If 2 moles of NO react with 1 mole of Cl2 to form 2 moles of NOCl, then a decrease of 0.36 M in NOCl indicates a decrease of 0.18 M each in NO and Cl2 based on the stoichiometry of the reaction. Therefore, the equilibrium concentrations of NO and Cl2 would be ([NO] = 0.61 M - 0.18 M = 0.43 M) and ([Cl2] = 0.57 M - 0.18 M = 0.39 M) respectively.

Now, we can use the equilibrium concentrations to calculate Kc:

Kc = [NOCl]^2 / ([NO]^2 × [Cl2])

Kc = (0.36 M)^2 / (0.43 M)^2 × 0.39 M)

Kc = 0.1296 M^2 / (0.1849 M^2 × 0.39 M)

Kc = 0.1296 M^2 / 0.072111 M^3

Kc = 1.798 (rounded off to three significant figures)

Therefore, the closest answer from the choices given is b) 1.58.