Chemistry Thermochemistry SZABMU 2024
PMDC Verified Question 4 of 81
Who stated that enthalpy change in a chemical reaction is same whether the reaction takes place in single step or in several steps?
A
Arrhenius' Law
B
Born Haber's Law
C
Hess's Law
D
Dalton'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 C: Hess's Law
Concept:

Thermochemistry relies heavily on state functions. Because enthalpy is a state function, its total change is route-independent.

Formula:

$$ \Delta H_{\text{direct}} = \Sigma \Delta H_{\text{indirect steps}} $$

Solution:

  • Germain Hess formalized this observation in 1840.


  • Hess's Law of Constant Heat Summation explicitly states that the total enthalpy change for a chemical reaction is identical regardless of how many steps or intermediate stages the reaction takes to complete.


Why other options are incorrect:

Arrhenius' Law relates reaction rates to temperature. The Born-Haber cycle is an application of Hess's Law. Dalton's Law deals with partial pressures of non-reacting gases.

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