Question

The reduced pressure of a gas is the ratio of its:
(A) actual pressure and critical pressure.
(B) pseudocritical pressure to pressure.
(C) critical pressure to pressure.
(D) pressure to pseudocritical pressure.

Answer 1

Hint : In thermodynamics, reduced properties are defined as a set of state variables for a fluid system that describes the properties of that fluid at the critical point. In thermodynamics, we define this critical point as the endpoint of the equilibrium curve.

Complete step by step answer
Gas has the ability to flow. The reduced pressure of the gas is a state variable that is used to describe the thermodynamic state of the system normalized by the gas properties at the critical point. Reduced pressure is one of the state variables of the reduced properties which is used to provide a precise accuracy near the critical state in that thermodynamic system of the fluid.
The critical pressure of the gas is defined as the point of temperature and pressure at which the liquid state coexists simultaneously with its vapor phase. At a temperature above the critical point, you cannot liquify it with any amount of pressure. The critical pressure is represented by the symbol $'{p_c}'$ . The reduced pressure of a gas is obtained by dividing the actual value of pressure on the value of critical pressure. Hence, it is given as the ratio of actual pressure to the critical pressure.
Therefore, option (A) is correct.

Additional information:
Other than reduced pressure, one reduced property of fluids is the reduced temperature. It is defined as the ratio of actual temperature to the value of critical temperature.

Note:
The value of critical pressure of any fluid is given as the value of its vapour pressure at the critical point. When you approach the critical point, the gaseous phase and liquid phase become one and their properties also become the same.