Problem 26 - Chemistry in 30 days

Question

\(\mathrm{CaCO}_{3}=\mathrm{CaO}+\mathrm{CO}_{2}\) reaction in a lime kiln goes to completion because (a) \(\mathrm{CaO}\) does not react with \(\mathrm{CO}_{2}\) to give \(\mathrm{CaCO}_{3}\) (b) Backward reaction is very slow (c) \(\mathrm{CO}_{2}\) formed escapes out (d) None of these

Step-by-Step Solution

Answer

(c) \( \mathrm{CO}_{2} \) formed escapes out.

Step 1: Understand the chemical reaction

The reaction given is \( \mathrm{CaCO}_{3} \rightarrow \mathrm{CaO} + \mathrm{CO}_{2} \), which is the thermal decomposition of calcium carbonate (limestone) into calcium oxide (lime) and carbon dioxide gas.

Step 2: Identify the nature of the reaction

In this reaction, \( \mathrm{CaCO}_{3} \) decomposes when heated, and \( \mathrm{CO}_{2} \) is released as a gas. This makes the reaction favorable to continue to completion as the product \( \mathrm{CO}_{2} \) is removed from the reaction mixture.

Step 3: Evaluate the given options

Option (a) is incorrect because \( \mathrm{CaO} \) can react with \( \mathrm{CO}_{2} \) to reform \( \mathrm{CaCO}_{3} \) under certain conditions. Option (b) is partially correct but not the main reason. Option (c) correctly identifies that \( \mathrm{CO}_{2} \) escaping drives the reaction forward by Le Chatelier's principle. Option (d) is incorrect as option (c) provides a suitable explanation.

Step 4: Determine the most accurate explanation

Considering the options, option (c) is the most accurate because the removal of \( \mathrm{CO}_{2} \) from the reaction environment prevents the reverse reaction and shifts the equilibrium towards the formation of \( \mathrm{CaO} \) and \( \mathrm{CO}_{2} \), allowing the reaction to go to completion.

Key Concepts

Decomposition Reaction

A decomposition reaction is a type of chemical reaction where one compound breaks down into two or more simpler substances. This is an essential concept in chemistry as it helps in understanding how complex molecules transform under various conditions. In decomposition reactions, a single compound acts as a reactant, and the outcome is multiple products.

One common form of decomposition reaction occurs when compounds are heated. Heat provides the energy necessary to break the chemical bonds holding the compound together. This leads to the formation of new substances.

• Example: In the reaction of calcium carbonate ( CaCO_3 ), heat causes it to break down into calcium oxide ( CaO ) and carbon dioxide ( CO_2 ).
• This type of reaction is significant in various industrial processes, such as the production of lime from limestone.

The thermal decomposition of calcium carbonate is a classic example, serving practical and educational purposes in understanding decomposition reactions and their applications.

Le Chatelier's Principle

Le Chatelier's Principle is a fundamental concept in chemical equilibrium that predicts how a system at equilibrium will respond to changes in concentration, temperature, volume, or pressure. It states that if a dynamic equilibrium is disturbed by changing the conditions, the system adjusts itself to partially oppose the effect of the disturbance, thereby reaching a new equilibrium.

For the thermal decomposition of calcium carbonate:

• Consider the reaction CaCO_3 ightarrow CaO + CO_2 . Here, the escape of CO_2 gas is vital. When CO_2 is continuously removed from the system, the equilibrium shifts towards the right, promoting the production of more CO_2 and CaO .
• This shift prevents the reactants from re-forming, allowing the reaction to proceed to completion.

Thus, understanding Le Chatelier's Principle helps explain why reactions, like the decomposition of calcium carbonate, tend to complete when gaseous products are continuously removed from the system.

Calcium Carbonate Decomposition

Calcium carbonate decomposition is a significant process both naturally and industrially. Naturally, this process occurs in geological formations, such as limestone caves, through long-term exposure to heat and other environmental conditions.

The chemical equation for the decomposition is:\[\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2\]

In industrial settings, such as in lime kilns, calcium carbonate is heated to a high temperature, leading to its breakdown. The process results in the formation of calcium oxide, known as quicklime, and the release of carbon dioxide gas.

• This decomposition is crucial in steelmaking, glass production, and cement manufacturing.
• Harvesting of CaO is beneficial for using it as a building material and in chemical production processes.

Understanding the decomposition of calcium carbonate is vital for both material science and environmental studies, as it plays a role in various ecological and industrial processes.