Specific Heat of a Gas

Specific heat is the amount of heat energy required to raise the temperature of one unit mass of a substance by one degree Celsius. This property is specific to each substance and is measured in units of J kg-1 °C-1. The specific heat of a gas depends on its molecular structure and its state of matter (solid, liquid, or gas).

Types of Specific Heat

There are two types of specific heat:

1. Specific Heat at Constant Volume (Cv)

The specific heat at constant volume is the amount of heat energy required to raise the temperature of one unit mass of a gas by one degree Celsius at constant volume. This means that the gas is not allowed to expand or contract during the heating process.

2. Specific Heat at Constant Pressure (Cp)

The specific heat at constant pressure is the amount of heat energy required to raise the temperature of one unit mass of a gas by one degree Celsius at constant pressure. This means that the gas is allowed to expand or contract during the heating process.

Answer Explanation

The correct answer to the question is option 'B' because gases have two specific heats: specific heat at constant volume (Cv) and specific heat at constant pressure (Cp). This is because gases are highly compressible and expandable, and their specific heat depends on whether the volume or pressure is kept constant during heating.

Cv is always less than Cp because the gas does not do any work during heating when the volume is kept constant. In contrast, when the pressure is kept constant, the gas does work against the external pressure, which increases the amount of heat energy required to raise the temperature.

Therefore, the specific heat of a gas depends on whether the volume or pressure is kept constant during heating, and gases have two specific heats instead of one.