Question

The temperature at which the physical properties of liquid and vapour become identical is called (1) absolute temperature (2) critical temperature (3) reduced temperature (4) transition temperature

Short answer

Critical temperature.

Step-by-step solution

Understanding the Terms

To solve this problem, it's important to understand the given terms: absolute temperature, critical temperature, reduced temperature, and transition temperature.

Define Absolute Temperature

Absolute temperature is a temperature measured on the Kelvin scale, starting from absolute zero. It is not related to the point where liquid and vapour properties become identical.

Define Critical Temperature

Critical temperature is the temperature above which a gas cannot be liquefied, regardless of the applied pressure. At this temperature, the physical properties of a liquid and vapour become identical.

Define Reduced Temperature

Reduced temperature is a dimensionless temperature obtained by dividing the actual temperature of a substance by its critical temperature. It is a ratio and not the point where liquid and vapour properties become identical.

Define Transition Temperature

Transition temperature refers to the temperature at which a substance changes from one phase to another, such as from solid to liquid. It is not specifically about liquid and vapour properties becoming identical.

Determine the Correct Answer

From the definitions, it's clear that the temperature at which the physical properties of liquid and vapour become identical is the critical temperature.

Key concepts

Physical properties of liquid and vapour

The physical properties of liquids and vapors are distinct under normal conditions. Liquids have a definite volume but no definite shape, conforming to their container. Vapors, on the other hand, expand to fill their container completely and have neither definite volume nor definite shape. At the critical temperature, these properties become indistinguishable. This means that liquid and vapour phases merge into a single phase, where both density and physical behavior are identical. The transition to this state is crucial in understanding how substances behave under different temperatures and pressures.

Absolute Temperature

Absolute temperature is measured on the Kelvin scale, starting from absolute zero, which is the point where no thermal energy is present. This is crucial in thermodynamics because it allows for the calculation of energy and behavior of particles in a more consistent manner across different substances. When discussing temperature in relation to phases and properties of materials, absolute temperature provides a more accurate measure of the thermal conditions.

Reduced Temperature

Reduced temperature is a dimensionless measure that helps in comparing the properties of substances at various temperatures relative to their critical temperature. It is calculated using the formula: \[ T_r = \frac{T}{T_c} \]where \( T \) is the actual temperature and \( T_c \) is the critical temperature. This ratio allows scientists to predict the behavior of substances under varying thermal conditions without needing specific temperatures, thus making it a powerful tool in thermodynamics and phase studies.

Transition Temperature

Transition temperature is the temperature at which a substance changes phase, such as from solid to liquid (melting point) or liquid to gas (boiling point). It’s different from the critical temperature, as it refers more generally to any phase change juncture. Each substance has its specific transition temperatures that dictate its state under given thermal conditions. Understanding these temperatures is essential for practical applications like refrigeration, metallurgy, and even cooking, where phase changes are pivotal.