Question

Positive entropy of a thermodynamic system indicates

• A. Heat addition to the system
• B. Heat rejection by the system
• C. No addition or rejection of heat to or from the system
• D. Entropy is not related to rejection or addition of heat

Hint:

Sign conventions in Thermodynamics:
$\delta Q > 0$ (Heat added) $\implies dS > 0$ (Entropy increases)
$\delta Q < 0$ (Heat rejected) $\implies dS < 0$ (Entropy decreases).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Entropy is a thermodynamic state property that measures the microscopic disorder or unavailability of thermal energy in a system. According to the Second Law of Thermodynamics, reversible heat transfer determines the change in entropy.
Key Formula or Approach:
\[ dS = \frac{\delta Q_{\text{rev}}}{T} \]

Step 2: Detailed Explanation:
From the Clausius definition of entropy:
\[ dS = \frac{\delta Q_{\text{rev}}}{T} \]
where \(T\) is absolute temperature (always positive, \(T > 0\) K).
- When heat is added to the system (\(\delta Q > 0\)), the change in entropy is positive (\(dS > 0\)).
- When heat is rejected by the system (\(\delta Q < 0\)), the change in entropy is negative (\(dS < 0\)).
- For an adiabatic reversible process (\(\delta Q = 0\)), entropy remains constant (\(dS = 0\)).

Step 3: Final Answer:
Hence, positive entropy change indicates heat addition to the system, matching option (A).