Question

Which of the following statements is NOT true in relation to a system that has reached the critical temperature?

• A. Substances can have more than one critical temperature.
• B. A surface between the liquid and vapour phases is no longer present.
• C. The system can be described as a homogenous fluid
• D. The system must a closed system

Answer 1

The correct option is A Substances can have more than one critical temperature.

The critical temperature is reached by heating a liquid in a closed system until the point where the density of the liquid is equal to the density of the vapour. At this point the interface between the liquid and vapour disappears resulting in a homogeneous fluid. This can only occur in a closed system (otherwise the vapour would escape into the surroundings) and each substance has a single critical temperature.