The Question is from NEET guide , and it was created by the author SUBHANI

Question

For a real gas undergoing an adiabatic free expansion (expansion against zero external pressure), which of the following statements is always true?

SUBHANI · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Adiabatic free expansion of a real gas
 **Related Topics**: Thermodynamics, internal energy, enthalpy, adiabatic process
 **Prerequisites**: Understanding of internal energy, enthalpy, adiabatic processes, and the concept of free expansion.
## SOLUTION PATHWAY
**Given Information**:
  * Adiabatic process: No heat exchange with the surroundings ($q = 0$)
  * Free expansion: No external pressure ($P_{ext} = 0$)
  * Real gas:  Deviations from ideal gas behavior are considered.
**Method & Steps**:
 1. Analyze the first law of thermodynamics.
  Reasoning: The first law of thermodynamics states that the change in internal energy ($\Delta U$) of a system is equal to the heat added to the system ($q$) minus the work done by the system ($w$).  Mathematically:
  Formula/Rule: $\Delta U = q + w$
 2. Apply the conditions of adiabatic free expansion.
  Working: Since the process is adiabatic, $q = 0$. Since it's a free expansion, the external pressure is zero, meaning no work is done by the gas against external forces ($w = 0$).  Therefore:
  $\Delta U = 0 + 0 = 0$
  Key Point: For an adiabatic free expansion, the internal energy of the gas remains constant, regardless of whether the gas is ideal or real.
 3. Evaluate the options.
  Result: The internal energy of the gas remains constant.
  Verification: The result is consistent with the first law of thermodynamics under the given conditions.
 ## OPTION ANALYSIS
A :x: The temperature change depends on the intermolecular forces in a real gas.  For an ideal gas, the temperature remains constant, but for a real gas, it can slightly increase or decrease depending on the nature of the intermolecular interactions. It's not *always* true.
B :x:  Similar to A, temperature change is not always guaranteed for a real gas undergoing adiabatic free expansion.
C ✓: The internal energy remains constant due to the absence of heat transfer and work done.
D :x: Enthalpy ($H = U + PV$) may change because the volume changes during expansion, even if the internal energy ($U$) remains constant.  
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Assuming the temperature remains constant: For real gases, the temperature may change slightly due to intermolecular interactions.
  2.Confusing adiabatic free expansion with other types of expansions (e.g., isothermal expansion): This leads to incorrect application of thermodynamic principles.
 **Quick Tips**:
  1. Remember the first law of thermodynamics ($\Delta U = q + w$) as the fundamental starting point for solving such problems.
  2. For adiabatic free expansion, always remember $q=0$ and $w=0$, implying $\Delta U = 0$.

SUBHANI · Answer

The temperature of the gas increases.

SUBHANI · Answer

The temperature of the gas decreases.

SUBHANI · Answer

The correct Option is "The internal energy of the gas remains constant."

SUBHANI · Answer

The enthalpy of the gas increases.

NEET Questions

Select Subject

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

Question Tags

NEET Subjects

Our Bots

Company