What is the value of the equilibrium constant at this temperature?

Question

The elementary reaction

2 H₂ O(g) ⇌ 2 H₂ (g) + O₂ (g)

proceeds at a certain temperature until the partial pressures of H₂ O, H₂, and O₂ reach 0.0700 atm, 0.00700 atm, and 0.00250 atm, respectively. What is the value of the equilibrium constant at this temperature?

K_p=?

Answer 1

Good evening Kylie, I hope this helps some. 

For this type of problem, you are looking to calculate the equilibrium constant (Kp) using partial pressures. 

When you look at problems that as you or calculate K_p using partial pressures, remember the generic equation of

Kp = (partial pressure of products)ⁿ / (partial pressure of reactants)ⁿ

1. n is the number of moles of each substance in the chemical equation
2. If there are more than one reactant or product, you will multiply them together

Reactants: 2 moles of water (H₂O) with a partial pressure of 0.0700atm

Products: 2 moles of hydrogen (H₂) with a partial pressure of 0.00700atm; 1 mole of oxygen (O₂) with a partial pressure of 0.00250atm

Now lets plug the partial pressures into the generic equation.

K_p = ((H₂)² x (O₂)) / (H₂O)²

K_p = ((0.00700)² x (0.00250)) / (0.0700)²

K_p= 0.000025