Question

The reduced pressure of a gas is the ratio of its:
(A) Actual pressure and its critical pressure
(B) Pseudocritical pressure to pressure
(C) Critical pressure to pressure
(D) Pressure to Pseudocritical pressure

Answer 1

Hint: Reduced pressure of a fluid depends upon the pressure at a point which is the end point in a phase equilibrium curve. The value of reduced pressure of a fluid depends upon the value of its actual pressure.

Complete step by step solution:
Here, we will know about the reduced pressure of a gas.
- We know that pressure is a thermodynamic parameter.
- Reduced properties of a gas are a set of certain kinds of state variables which depends upon the state properties of the gas at its critical point. This is not only true for the gases but also it is seen in liquids. We already know that critical point is the end point in a phase equilibrium curve.
- Reduced pressure is defined as the ratio of its actual pressure to the critical pressure of the fluid. The relation can be expressed in terms of the equation as below.
\[{p_r} = \dfrac{p}{{{p_c}}}\]
Here, ${p_r}$ is the reduced pressure, p is the actual pressure and ${p_c}$ is the critical pressure of the fluid.
- Critical pressure is the pressure corresponding to the critical point of the fluid in the phase diagram.
- Pseudocritical pressure is the molal average critical pressure in the system. So, it is not used to calculate reduced pressure.
- So, we can conclude that the reduced pressure of a gas in the ratio of its actual pressure and its critical pressure.

Therefore, we can say that the correct answer if this question is (A).

Note: Remember that Pseudocritical pressure and critical pressure of a gas are different quantities. Pseudocritical pressure is the molal average critical pressure in the system. Critical pressure is the pressure corresponding to the critical point of a fluid.