Question

Identify the correct variation of pressure and volume of a real gas (A) and an ideal gas (B) at constant temperature.
(\(y=P;\;x=V\))

• A. Graph 1
• B. Graph 2
• C. Graph 3
• D. Graph 4

Hint:

At constant temperature: \[ PV=\text{constant} \] for an ideal gas. Real gases generally show lower pressure than ideal gases due to intermolecular attractions.

Answer 1

The Correct Option is C

Step 1: Recall Boyle's Law for ideal gases at constant temperature.
For an ideal gas: $PV = \text{constant}$, so $P \propto 1/V$. The P-V graph is a smooth rectangular hyperbola.
Step 2: Understand sources of deviation in real gases.
Real gases deviate due to intermolecular attractive forces and finite molecular volume. The direction of deviation depends on the pressure range.
Step 3: Describe behaviour at moderate pressures.
At moderate pressures, attractive forces dominate. Real gas pressure is slightly lower than ideal for the same volume. The real gas curve dips below the ideal hyperbola.
Step 4: Describe behaviour at very high pressures.
At very high pressures, repulsive forces and finite molecular volume dominate. Real gas pressure exceeds ideal pressure. The real gas curve rises above the ideal curve.
Step 5: Identify Graph 3 as the correct representation.
Graph 3 shows real gas curve (A) dipping below ideal curve (B) at moderate pressures and rising above it at high pressures. Other graphs show physically incorrect trends.
Step 6: State the final answer.
\[ \boxed{\text{Graph 3}} \]