Question

Bomb calorimeter is used to determine the heat of reaction at (1) constant pressure (2) constant volume (3) \(298 \mathrm{~K}\) (4) \(373 \mathrm{~K}\)

Short answer

The bomb calorimeter determines the heat of reaction at constant volume.

Step-by-step solution

Identify the features of a bomb calorimeter

A bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of combustion of a particular reaction. The key feature to remember is its constant volume.

Analyze provided options

Given the options: (1) constant pressure, (2) constant volume, (3) 298 K, and (4) 373 K. Recall that a bomb calorimeter operates at constant volume.

Choose the correct answer

Since the bomb calorimeter works at constant volume, the correct option is (2) constant volume.

Key concepts

Heat of Reaction

In thermodynamics, a heat of reaction is the heat change that occurs when a specified chemical reaction takes place. It can either be exothermic (releasing heat) or endothermic (absorbing heat). The heat of reaction is a crucial concept because it tells us about the energy change during a chemical process.
Understanding this helps in predicting reaction behavior and calculating energy requirements or releases in industrial processes.
The heat of reaction is typically measured in Joules (J) or calories (cal), and is often determined using a calorimeter.

• In an exothermic reaction, the surroundings get warmer.
• In an endothermic reaction, the surroundings get cooler.

The specific value of the heat of reaction for a process can be determined using devices such as a bomb calorimeter, which measures the heat at constant volume.

Constant Volume

A key feature of a bomb calorimeter is that it operates at constant volume.
This means that no work is done by or on the system in terms of expansion or compression since the volume does not change.

• No volume change leads to precise measurement of the heat involved.
• It makes the calculations simpler because the only concern is the internal energy change.

During the reaction, the calorimeter absorbs the heat released or supplies the heat absorbed, ensuring the measurement is accurate by maintaining a constant volume.

Chemical Thermodynamics

Chemical thermodynamics explores the energy changes during chemical reactions and how these changes affect system properties.
It provides a framework to understand how energy is transferred and transformed.
In the context of a bomb calorimeter:

• The system remains isolated from its surroundings.
• The energy changes are confined to the chemical reaction inside the apparatus.

Basic principles such as the first law of thermodynamics (energy conservation) apply. This principle asserts that the total energy of an isolated system is constant, providing foundational knowledge for calculating reaction heats and understanding how energy is conserved in chemical processes.