Chemistry 30

Write equilibrium expressions for the following reversible reactions:

For the equilibrium system described by 2 SO_{2 (g)} + O_{2 (g)} ↔ 2 SO_{3 (g)}

at a particular temperature the equilibrium concentrations of SO₂, O₂ and SO₃ were 0.75 M, 0.30 M, and 0.15 M, respectively. At the temperature of the equilibrium mixture, calculate the equilibrium constant, K_eq, for the reaction.

Solution:

For the equilibrium system described by: PCl_{5 (g)} ↔ PCl_{3 (g)} + Cl_{2 (g)}

K_eq equals 35 at 487°C. If the concentrations of the PCl₅ and PCl₃ are 0.015 M and 0.78 M, respectively, what is the concentration of the Cl₂?

Solution:

Again begin by setting up the equilibrium constant for the equation and then substitute in the known values. But in this case, K_eq is one of our known values; one of the concentrations is the unknown.

The following table gives some values for reactant and product equilibrium concentrations (in moles/L; M) at 700 K for the Shift reaction, an important method for the commercial production of hydrogen gas: CO_(g) + H₂O_(g) ↔ CO_{2 (g)} + H_{2 (g)}

Calculate K_eq for each of the five trials. How do the answers compare with each other? Why?

Solution:

Set up the equilibrium constant expression and solve for K_eq for each trial.

K_eq = 5.09 for all trials.

K_eq is a constant and will not change unless the temperature of the system is changed (there are often minor variations resulting from experimental measurements, however).

return to notes