A gas can be liquefied

Options

A. At any temperature
B. Above its critical temperature
C. At its critical temperature
D. Below its critical temperature

Answer

To solve the question regarding the liquefaction of gases, we need to understand the concepts of ideal and real gases, as well as the significance of critical temperature. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Difference Between Ideal and Real Gases
- **Ideal Gas**: An ideal gas follows the ideal gas law perfectly and does not exhibit any intermolecular forces. Hence, it cannot be liquefied under any conditions.
- **Real Gas**: A real gas, on the other hand, has intermolecular forces that allow it to be liquefied under certain conditions.

**Hint**: Remember that ideal gases do not have attractive forces, while real gases do.

### Step 2: Identify the Conditions for Liquefaction
- For a gas to be liquefied, it must be subjected to conditions where the intermolecular forces can overcome the kinetic energy of the molecules. This typically occurs at high pressures and low temperatures.

**Hint**: Think about how pressure and temperature affect the state of matter.

### Step 3: Understand the Role of Critical Temperature
- The critical temperature is the maximum temperature at which a gas can be converted to a liquid. Above this temperature, no amount of pressure can liquefy the gas.
- If the temperature of the gas is below its critical temperature, it can be liquefied by applying sufficient pressure.

**Hint**: Focus on the concept of critical temperature; it’s crucial for determining whether a gas can be liquefied.

### Step 4: Analyze the Pressure-Volume Graph
- In a pressure versus volume graph for a real gas, there are distinct regions:
- **Low Pressure Region**: Gas phase only.
- **High Pressure Region**: Liquid and vapor coexist.
- **Critical Point**: The point at which the distinction between liquid and vapor disappears.

**Hint**: Visualize the graph and the regions to understand where liquefaction occurs.

### Step 5: Conclusion
- To liquefy a gas, it is essential that the gas is below its critical temperature. Therefore, the answer to the question is that a gas can be liquefied if its temperature is below the critical temperature.

**Hint**: Always check the conditions (temperature and pressure) when considering the state of a gas.

### Final Answer
A gas can be liquefied if its temperature is below its critical temperature.