Chemistry Thermochemistry DUHS 2023
PMDC Verified Question 30 of 81
What is \( \Delta H \) equal to —— according to the first law of thermodynamics?
A
\( \Delta E + P\Delta V \)
B
\( \Delta E - P\Delta V \)
C
\( -\Delta E - P\Delta V \)
D
\( -\Delta E + P\Delta V \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: \( \Delta E + P\Delta V \)
Concept:

Enthalpy (\( H \)) is a state function defined fundamentally as internal energy plus pressure-volume energy.

Formula:

$$ H = E + PV $$

Solution:

  • If a thermodynamic process occurs at constant pressure, the change in enthalpy is given by taking the delta of the definition:


  • $$ \Delta H = \Delta E + P\Delta V $$


  • This directly aligns with the First Law when substituting heat at constant pressure (\( q_p = \Delta H \)) and expansion work (\( w = -P\Delta V \)): \( \Delta E = \Delta H - P\Delta V \), which rearranges to the same equation.


Why other options are incorrect:

Option B uses a negative sign which contradicts the definition of enthalpy. Options C and D improperly apply negative signs to the internal energy term.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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