Which of the following is the best definition of Hess' Law?
A. Heat is always released by the decomposition of 1 mole of a compound into its constitute elements.
B. Since enthalpy is a state function, it will be different if a reaction takes place in one step or a series of steps.
C. Heat evolved in a given process can be expressed as the sum of the heats of several processes that, when added, yield the process of interest.
D. The enthalpy of a process is the difference between the enthalpy of the products and the enthalpy of the reactants.
E. At constant pressure the enthalpy change of a reaction is equal to the heat change of a reaction.
D sounds pretty good.
is it C?
C
C, I think.
The correct answer is C. Hess' Law states that the heat evolved in a given process can be expressed as the sum of the heats of several processes that, when added, yield the process of interest.
To determine the correct definition, let's understand the process of elimination used to select the correct answer:
A. Heat is always released by the decomposition of 1 mole of a compound into its constitute elements. This answer is incorrect because it describes the heat released during the decomposition of a compound, rather than the concept of Hess' Law.
B. Since enthalpy is a state function, it will be different if a reaction takes place in one step or a series of steps. This answer is incorrect because it describes the relationship between enthalpy and the number of steps in a reaction, rather than the concept of Hess' Law.
C. Heat evolved in a given process can be expressed as the sum of the heats of several processes that, when added, yield the process of interest. This answer is correct and accurately describes the concept of Hess' Law. It explains that the heat evolved or absorbed during a chemical reaction can be determined by adding up the individual heats of distinct processes.
D. The enthalpy of a process is the difference between the enthalpy of the products and the enthalpy of the reactants. This answer is incorrect because it describes the concept of enthalpy rather than Hess' Law. While the enthalpy difference plays a role in Hess' Law, it is not a comprehensive definition of the law itself.
E. At constant pressure, the enthalpy change of a reaction is equal to the heat change of a reaction. This answer is incorrect because it describes the relationship between enthalpy change and heat change at constant pressure, rather than the concept of Hess' Law.
In summary, Hess' Law (option C) is the best definition because it accurately explains how the heat evolved in a given process can be expressed as the sum of the heats of several processes that, when added, yield the process of interest.