Question

At a certain temperature, the K_p for the decomposition of H₂S is 0.842.
H₂S(g) H₂(g) + S(g)
Initially, only H₂S is present at a pressure of 0.104 atm in a closed container. What is the total pressure in the container at equilibrium?

I know:
          H₂S(g) H₂(g) + S(g)

Initial: 0.104 atm         0 atm    0 atm
change: -x                      x           x
final:   0.104 -x             x           x

0.842 =
0.842 =

x² + 0.842 x - 0.0876 = 0

0.109 is greater than the initial concentration of 0.104 so it cannot be used.
x = -0.95

total pressure = equlibrium pressure of H₂ + equilbrium pressure H₂S + equilibrium pressure of S

total pressure = 0.104 - (-0.95) + (-0.95) + (-0.95)

total pressure = -0.846

This is incorrect because the total concentration must be greater than the initial concentration of 0.104 atm. 

Answer 1

Concepts and reason

The concepts used to solve this problem chemical equilibrium.

A chemical reaction attains the stage of equilibrium when carried out in a closed vessel. In chemical equilibrium, the rate of the forward reaction becomes equal to the rate of backward reaction which results in no net changes in the concentration of reactants and products.

Fundamentals

As defined by the Law of chemical equilibrium, the ratio of the product of the partial pressure of reaction product raised to the respective stoichiometric coefficient to the product of the concentration of reactant raised to the respective stoichiometric coefficient has a constant value. The constant value is known as equilibrium constant. For the gaseous reaction, equilibrium constant is denoted by .

Consider the following equation for a gas-phase reaction:

Using Law of chemical equilibrium, the relation between partial pressure of reactant and product is:

Consider the reaction:

Initial partial pressure of is 0.104 and equilibrium constant, is 0.842

ICE table for the reaction is:

Use the expression:

Substitute 0.842 for , x for and x for

On solving, the equation is:

The value of x is solved by using the quadratic equation:

Substitute 0.842 for b, 1 for a and 0.0876 for c and solve the equation:

= 0.0936 or -0.936

The values for x is 0.0936

As per the ICE table:

Equilibrium partial pressure of , is 0.104 – x

Substitute x as 0.0936

= 0.104 - 0.0936

is 0.0104 atm.

Equilibrium partial pressure of , is x

Substitute x as 0.0936

is 0.0936 atm

Equilibrium partial pressure of , is x

Substitute x as 0.0936

is 0.0936 atm

Total pressure is the sum of partial pressure of gases in the reaction mixture.

Hence, total pressure for the given reaction at equilibrium is:

Substitute 0.11 for ,0.0936 for and 0.0936 for

Ans:

The total pressure at equilibrium for the given reaction is 0.198 atm.

[Answer Choice End]

[Answer Choice: Wrong]

The total pressure at equilibrium for the given reaction is -0.831 atm