Chemistry Thermochemistry ETEA 2024
PMDC Verified Question 13 of 81
\( \Delta H \) can be measured indirectly by applying:
A
Faraday's law
B
Hess's law
C
Avogadro's law
D
Gas's law
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Hess's law
Concept:

Direct measurement of enthalpy change (via calorimetry) is often physically impossible due to dangerous reaction conditions, extreme slowness, or unwanted side products.

Solution:

  • To solve this, scientists calculate the enthalpy change indirectly using known standard values from other reactions.


  • This is accomplished strictly through Hess's law, which guarantees that summing the enthalpies of multiple indirect steps will yield the exact same \( \Delta H \) as the direct impossible reaction.


Why other options are incorrect:

Faraday's laws govern electrolysis and charge transfer. Avogadro's and general gas laws govern physical states of matter, not thermochemical energy tracking.

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