Question

The falsc statement among the following is (1) A reversible reaction never goes to completion. (2) A reversible reaction attains equilibrium when Gibbs energy change accompanying the reaction is zero. (3) The reaction between barium chloride and sodium sulphate goes to completion because barium sulphate formed is insoluble. (4) The rate of forward reaction in a reversible reacfion increases as the reaction proceeds.

Short answer

Option (4) is the false statement.

Step-by-step solution

Identify key concepts

Understand the nature of reversible reactions, incomplete reactions, equilibrium, Gibbs energy, and chemical reaction completion.

Analyze option (1)

A reversible reaction never goes to completion, which is true because it can achieve equilibrium where both forward and backward reactions continue to occur at equal rates.

Analyze option (2)

A reversible reaction attains equilibrium when Gibbs energy change accompanying the reaction is zero, which is true because the system has reached a state of minimum Gibbs free energy, indicating equilibrium.

Analyze option (3)

The reaction between barium chloride and sodium sulphate goes to completion because barium sulphate formed is insoluble, which is true because the formation of an insoluble product drives the reaction to completion.

Analyze option (4)

The rate of the forward reaction in a reversible reaction increases as the reaction proceeds, which is false. In a reversible reaction, as the reaction proceeds, the rate of the forward reaction decreases and the rate of the backward reaction increases until equilibrium is reached.

Conclusion

Evaluate all options: Options (1), (2), and (3) are correct, but option (4) is incorrect as it contradicts the principles of reversible reactions.

Key concepts

Reversible Reactions

In chemistry, a reversible reaction is a chemical reaction where the reactants form products that, in turn, react together to give the reactants back. These reactions do not generally go to completion.
Instead, they reach a state of equilibrium where the rates of the forward and backward reactions are equal. Because of this, both reactants and products are present in the system simultaneously.
Examples of reversible reactions include the synthesis of ammonia and the reversible hydration of ethene to ethanol. It’s crucial to understand that just because a reaction is reversible doesn't mean it can’t reach high conversions of reactants to products; it simply means that the backwards reaction remains possible under the conditions provided.

Gibbs Energy

Gibbs free energy, or G, is a thermodynamic potential that measures the maximum reversible work obtainable from a system at constant temperature and pressure. Its change, \(\text{ΔG}\), during a process determines the spontaneity of the process. If \(\text{ΔG} < 0\), the process occurs spontaneously.

At equilibrium, the change in Gibbs energy is zero (\(\text{ΔG} = 0\)). This means there is no net change in the amounts of reactants and products, and the system is in its most stable state.

Considering reversible reactions, when the Gibbs energy change reaches zero, it indicates that the system has balanced to the point where the forward and backward reactions happen at the same rate, maintaining equilibrium.

Reaction Completion

Reaction completion refers to a scenario where the reactants have been fully converted to products with no significant amount of reactants remaining. This can occur when a certain product of the reaction is removed from the system.

In some chemical reactions, especially in an open system or in reactions with an insoluble product, reactions proceed until the reactants are entirely transformed. An example is the reaction between barium chloride and sodium sulphate which results in the formation of insoluble barium sulphate (\(\text{BaSO}_4\)). The removal of \(\text{BaSO}_4\) from the reaction mixture forces the reaction to continue until one or more reactants are exhausted.

Insoluble Products

Insoluble products are compounds that do not dissolve appreciably in a solvent, typically water. When a chemical reaction produces an insoluble product, it can precipitate out of the solution, which can drive the reaction to completion.

For instance, in the reaction between barium chloride (\(\text{BaCl}_2\)) and sodium sulphate (\(\text{Na}_2\text{SO}_4\)), barium sulphate (\(\text{BaSO}_4\)) is formed as an insoluble precipitate.

This formation pulls the equilibrium towards the completion by continuously removing barium and sulphate ions from the solution, hence driving the reaction forward until the limiting reactant is depleted. This concept is essential in qualitative analysis and many industrial processes that rely on precipitation to purify substances or drive reactions to completion.