Question

In lime kiln, the reversible reaction \(\mathrm{CaCO}_{3}(\mathrm{~s}) \rightleftharpoons\) \(\mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{~g})\) proceeds to completion because (1) of high temperature (2) \(\mathrm{CO}_{2}\) escapes out (3) \(\mathrm{CaO}\) is removed (4) of low pressure

Short answer

(2) \text{CO}_{2} escapes out.

Step-by-step solution

Understand the Reaction

The given reversible reaction is \(\text{CaCO}_{3}(\text{s}) \rightleftharpoons \text{CaO}(\text{s}) + \text{CO}_{2}(\text{g})\). This represents the decomposition of calcium carbonate into calcium oxide and carbon dioxide gas.

Analyze Conditions for Completion

For a reversible reaction to proceed to completion, a factor must drive the reaction in one direction. Here, the formation of \(\text{CO}_{2}\) gas can help push the equilibrium towards the products.

Role of Gas Escaping

The escape of \(\text{CO}_{2}\) gas from the reaction site effectively reduces its concentration in the system. According to Le Chatelier's principle, the system will shift to produce more \(\text{CO}_{2}\) gas, pushing the reaction towards completion.

Choose the Correct Answer

Among the given options: (1) high temperature, (2) \(\text{CO}_{2}\) escapes out, (3) \(\text{CaO}\) is removed, and (4) low pressure — the correct answer is (2) \(\text{CO}_{2}\) escapes out, as this directly drives the reaction to completion.

Key concepts

Lime Kiln Reaction

The lime kiln reaction is a crucial chemical reaction used in various industrial processes. This reaction is represented as \( \text{CaCO}_{3}(\text{s}) \rightleftharpoons \text{CaO}(\text{s}) + \text{CO}_{2}(\text{g})\). Here, calcium carbonate (\text{CaCO}_{3}) decomposes into calcium oxide (\text{CaO}) and carbon dioxide (\text{CO}_{2}).
Calcium carbonate, a major component of limestone, undergoes thermal decomposition in a lime kiln heated to high temperatures. This process is endothermic, meaning it absorbs heat. As the limestone is heated, it breaks down, releasing carbon dioxide gas and leaving behind quicklime (calcium oxide):

• \( \text{CaCO}_{3} \rightarrow \text{CaO} + \text{CO}_{2}\)

The escaping carbon dioxide drives the reaction forward, ensuring that calcium carbonate is continuously converted into its products. This reaction has vast industrial significance, playing an essential role in the production of cement and the chemical industry.

Le Chatelier's Principle

Le Chatelier's Principle is a fundamental concept in chemical equilibrium. It states that if a system at equilibrium is disturbed by a change in concentration, temperature, or pressure, the system will shift its position to counteract that disturbance and restore balance.
In the context of the lime kiln reaction, when \( \text{CO}_{2}\) gas escapes, it disturbs the equilibrium. According to Le Chatelier's Principle, the reaction will shift towards the production of more \( \text{CO}_{2}\):

• As \( \text{CO}_{2}\) is removed from the system, the equilibrium shifts to the right, producing more \( \text{CaO}\) and \( \text{CO}_{2}\). This drives the reaction towards completion.
• High temperature also contributes by providing the necessary energy for decomposition.

Therefore, the principle helps us understand how external conditions affect reversible reactions, guiding us in optimizing industrial processes.

Calcium Carbonate Decomposition

Calcium carbonate decomposition is a key chemical reaction in the lime kiln process. This reaction involves the breakdown of calcium carbonate (\text{CaCO}_{3}) into calcium oxide (\text{CaO}) and carbon dioxide (\text{CO}_{2}) when heated.
Several factors influence this decomposition:

• Temperature: Higher temperatures provide the energy needed to break the bonds in calcium carbonate.
• Pressure: While lower pressure supports the release of \( \text{CO}_{2}\), in an industrial lime kiln, the escaping gas naturally lowers the partial pressure of \( \text{CO}_{2}\).
• Removal of \( \text{CaO}\): In some processes, continuously removing \( \text{CaO}\) can push the reaction forward, though it's less critical than the escape of \( \text{CO}_{2}\).

Understanding calcium carbonate decomposition helps in improving the efficiency of lime production, among other critical industrial uses.