Common household bleach is an aqueous solution containing hypochlorite ions. A closed container
of bleach is an equilibrium system represented by the equation below.
ch 17
Cl2(g) + 20H- (aq) = CIO-(aq) + Ci-(aq) + H2O(l)
4. Compare the rate of the forward reaction to the rate of the reverse reaction for this system.
5. State the effect on the concentration of he cio-ion when there is a decrease in the concentration of
the OH-ion.
6. Explain why the container must be closed to maintain equilibrium.

Explanation:

Question 4. Compare the rate of the forward reaction to the rate of the reverse reaction for this system.

The chemical equilibrium is a dynamic equilibrium. This means that the species in equilibrium are continuously changing but the change is such that there is no net (macroscopic) change.

How does this happen? It happens because the speed at which the reactants are consumed to generate the products, through the direct reaction, is the same speed as the opposite, through the reverse reaction.

The when you are asked to compare the rate of the forward reaction to the rate of the reverse reaction for this system, you must say that they are equal.

Question 5. State the effect on the concentration of the ClO⁻ ion when there is a decrease in the concentration of the OH⁻ ion.

When the system is in equilibrium, the equilibrium constant does not change, unless the temperature changes. Thus, when the concentration of one species changes, the concentration of the other species must change in a way that the equilibrium constant remain unchaged.

Since ClO⁻ ions and Cl⁻ ions are in the same side of the equation, if one changes the other must change in the inverse way, to keep the equilibrium constant unchanged. This is also stated by LeChatelier's principle: when a system in equilibrium is disturbed the system will react to counteract the disturbance and restablish the equilibrium.

If ClO⁻ decreases, the reaction will shift to the right by consuming more OH⁻ ions, and producing more Cl⁻ ions. Hence, the effect is the decrease of the OH⁻ ions.

Question 6. Explain why the container must be closed to maintain equilibrium.

The container must be closed to avoid the scape of Cl₂(g) to the atmosphere.

When Cl₂ (g) escapes, it causes the consumption of ClO⁻ (aq) and Cl⁻ ions by the reverse reaction, producing more Cl₂ (g), in a shift that seeks to restore the chemical equilibrium, but since Cl₂ (g) continues to escape, the equilibrium is never reached, and the ClO⁻ (aq) and Cl⁻ ions will be consumed until they are depleted from the system.

At the end, only water would remain in the container.

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