Question

Select the wrong option regarding enthalpy

• A. Enthalpy is the measure of total heat in a thermodynamic system where pressure is constant
• B. It is represented as \(\Delta H = \Delta E + P \Delta V\)
• C. It is a measure of disorder in a thermodynamic system
• D. It represents the heat constant of a system

Hint:

• Enthalpy \(H = E + PV\) (or \(U+PV\)).
• Change in enthalpy \(\Delta H = q_p\) (heat exchanged at constant pressure).
• For processes at constant pressure, \(\Delta H = \Delta E + P\Delta V\).
• Entropy (S) is the measure of disorder or randomness in a system.

Answer 1

The Correct Option is C

Enthalpy (H) is a thermodynamic property defined as \(H = E + PV\), where E is internal energy, P is pressure, and V is volume. Let's analyze the options:
(a) "Enthalpy is the measure of total heat in a thermodynamic system where pressure is constant": More precisely, the change in enthalpy (\(\Delta H\)) of a system at constant pressure is equal to the heat absorbed or released by the system (\(q_p\)). So, \( \Delta H = q_p \). While related to "total heat content" under constant pressure, this statement is largely considered TRUE in intent.
(b) "It is represented as \(\Delta H = \Delta E + P \Delta V\)": From \(H = E + PV\), if pressure P is constant, then \(\Delta H = \Delta E + \Delta(PV) = \Delta E + P\Delta V + V\Delta P\). If P is constant, \(\Delta P = 0\), so \(\Delta H = \Delta E + P\Delta V\). This is TRUE for constant pressure processes. (Note: \(\Delta E\) is often written as \(\Delta U\) for internal energy).
(c) "It is a measure of disorder in a thermodynamic system": This statement is FALSE. The measure of disorder or randomness in a thermodynamic system is Entropy (S), not enthalpy.
(d) "It represents the heat constant of a system": This phrasing is a bit vague. "Heat content" is a common informal term for enthalpy. If "heat constant" means heat content, then it aligns with the concept. Enthalpy is often referred to as the heat content at constant pressure.
The statement that is definitively wrong is (c). Enthalpy is related to heat content, especially at constant pressure, while entropy is the measure of disorder. \[ \boxed{\text{It is a measure of disorder in a thermodynamic system}} \]