Hess's law ____.
A. makes it possible to calculate [tex]\Delta H[/tex] for complicated chemical reactions
B. states that when you reverse a chemical equation, the sign of [tex]\Delta H[/tex] does not change
C. determines the way a calorimeter works
D. describes the vaporization of solids
Answer (3)
**A.) ** **makes it possible to calculate ΔH for complicated chemical reactions
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Hess’s Law makes it possible to calculate ΔH for complicated chemical reactions. Moreover, the principle claims that the entire amount of “enthalpy” when the development or progression of a chemical reaction is complete whether the reactions are created in a single or numerous processes, it still changes. This law is now described as the principle of conservation of energy, and part of the thermodynamics law as the first.
Hess's Law is a fundamental concept in chemistry that makes it possible to calculate ΔH for complicated chemical reactions. It operates on the principle that the total enthalpy change for a chemical process is the same, regardless of the pathway by which the chemical reaction takes place. Hess's Law states that if a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps. This law is valid because enthalpy is a state function, meaning enthalpy changes depend only on the initial and final states of the system, not on the path taken.
For example, if the enthalpy changes for forming products A and B from reactants C and D in a series of reactions are known, one can calculate the overall enthalpy change for the reaction of C with D to produce A and B. This capability is particularly useful for analyzing reactions that are too difficult to measure directly. Reversing a chemical reaction reverses the sign of ΔH, illustrating the dependency of enthalpy change on the direction of the reaction. However, this aspect is a separate consideration from Hess's Law itself, which focuses on the summation of enthalpy changes for steps in a reaction process.
Hess's Law allows researchers to calculate the change in enthalpy (ΔH) for complex chemical reactions by summing the changes across multiple steps. It highlights that enthalpy is a state function, meaning it is determined only by initial and final states, not by the path taken. The correct choice for the multiple choice question is A.
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