Question

Gas in cylinder with light piston is slowly heated till all the mercury spills over.
$P_{atm}=76cm$ of Hg column
Statement 1 : The temperature of gas continuously increases.
Statement 2: According to first law of thermodynamics $dQ=dU+dW$ where symbols have their usual meaning.

• A. Statement1 is true, statement 2 is true and statement 2 is correct explanation for statement 1
• B. Statement1 is true, statement 2 is true and statement 2 is NOT the correct explanation for statement 1
• C. Statement 1 is true statement 2 is false
• D. Statement 1 is false , statement 2 is true

Answer 1

Answer: (D)

Statement 1 is false , statement 2 is true

Change in temperature depends on what sort of process we allow the system to evolve through.
We only know that it is some sort of reversible expansion with decreasing pressure, i.e P decreases while V increases$\Rightarrow$ their product may increase or decrease or remain constant.

Applying ideal gas eqn. $PV=nRT$ , temperature may increase or decrease or remain constant.So statement a is false
Statement b is true as it is the statement of first law regarding conservation of energy.

Hence d is correct option