Question

What is meant by critical temperature?

Short answer

Answer: Critical temperature (Tc) is the temperature at which a material undergoes a continuous (second order) phase transition, meaning the substance changes its phase without a discontinuity in any of its physical properties. Critical temperature is significant in the context of phase transitions as it defines the boundary between two different phases of a material, allowing for an easy transition between them without consuming or releasing energy. Common examples include the boiling point of a liquid and superconducting phase transitions.

Step-by-step solution

Definition of Critical Temperature

The critical temperature, often denoted as Tc, is the temperature at which a material undergoes a continuous (second order) phase transition. In other words, at the critical temperature, a substance changes its phase without a discontinuity in any of its physical properties such as entropy, enthalpy, or specific heat capacity.

Phase Transitions and Critical Temperature

In the context of phase transitions, critical temperature is an important characteristic as it defines the boundary between two different phases of a material. It is at this temperature that the distinction between the two phases becomes indistinguishable, and the substance can easily transition between them without consuming or releasing energy.

Examples

A common example of critical temperature is the boiling point of a liquid. When a liquid reaches its critical temperature, it can transform into a gas without any latent heat release. For water, the critical temperature is approximately 374°C (707°F) and a pressure of 22.1 MPa. Another example of critical temperature is the superconducting phase transition, where a material transitions from a normal conducting state to a superconducting state with zero electrical resistivity. For example, the critical temperature for lead (Pb) is 7.2 K, and for mercury (Hg) is 4.2 K.