Question

The phase diagram of CO\(_2\) is shown below: 

Phase diagram of CO\(_2\) with solid, liquid, and gas phases labeled along with critical temperature \(T_c\) and triple point temperature \(T_1\) The correct statement(s) about CO\(_2\) is/are: 
 

• A. Below \( T_c \), it does not exist in liquid state.
• B. Above \( T_c \), it does not exist in liquid state.
• C. At \( T_c \), it can exist in all three phases.
• D. Above \( T_1 \), it does not exist in solid state.

Hint:

In phase diagrams, the critical point marks the temperature above which the liquid and gas phases merge into a supercritical fluid. Below the critical temperature, liquids and gases are distinct, and the triple point marks the condition where all three phases coexist.

Answer 1

The Correct Option is A, C

The phase diagram of CO\(_2\) shows the relationship between pressure and temperature, indicating the phases in which CO\(_2\) exists under various conditions. Step 1: Analyze each statement
- (A) Below \( T_c \), it does not exist in liquid state.
- Below the critical temperature \( T_c \), the liquid and gas phases are distinct, and CO\(_2\) can exist as a liquid only at certain pressures. Therefore, at temperatures lower than \( T_c \), CO\(_2\) cannot exist in a liquid state unless the pressure is above the triple point pressure \( P_1 \). Hence, this statement is true.
- (B) Above \( T_c \), it does not exist in liquid state.
- Above the critical temperature \( T_c \), CO\(_2\) enters a supercritical fluid phase where it does not have distinct liquid and gas phases. This statement is false because above \( T_c \), CO\(_2\) exists as a supercritical fluid, not as a gas or liquid. So, this statement is incorrect.
- (C) At \( T_c \), it can exist in all three phases. - At the critical temperature \( T_c \), CO\(_2\) can exist in all three phases (solid, liquid, and gas) in equilibrium at the triple point. Hence, this statement is true.
- (D) Above \( T_1 \), it does not exist in solid state.
- Above the triple point temperature \( T_1 \), CO\(_2\) cannot exist in the solid state because the temperature is too high for the solid phase to be stable. So, this statement is correct.
Thus, the correct answers are (A) and (C). Final Answer: (A) Below \( T_c \), it does not exist in liquid state.
(C) At \( T_c \), it can exist in all three phases.