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. The enthalpy of a process is the difference between the enthalpy of the products and the enthalpy of the reactants.
C. Since enthalpy is a state function, it will be different if a reaction takes place in one step or a series of steps.
D. 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.
E. At constant pressure the enthalpy change of a reaction is equal to the heat change of a reaction.
Did you look up on the internet what Hess'Law is? That might help?
Look up Hess' Law. See if it agrees with Statement D.
The best definition of Hess' Law is option D: "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 understand why this is the correct definition, let's break it down:
Hess' Law states that the total enthalpy change of a chemical reaction is independent of the pathway taken to reach the final products. In other words, it doesn't matter if a reaction occurs in one step or a series of steps, the overall enthalpy change (heat evolved or absorbed) remains the same.
To determine the enthalpy change of a reaction using Hess' Law, you need to look at the enthalpy changes of other reactions that can be combined to yield the reaction of interest. For example, if you want to calculate the enthalpy change for reaction A + B → C, but you don't have experimental data for that specific reaction, you can look for other reactions that involve A, B, and C. By adjusting the coefficients and reversing reactions, you can manipulate these reactions to match the desired reaction.
The key concept is that enthalpy change is a state function, meaning it depends only on the initial and final states of the reactants and products, regardless of the path taken. Thus, you can add and subtract the enthalpy changes of intermediate reactions to obtain the enthalpy change of the overall reaction, which is the essence of Hess' Law.
Therefore, option D correctly captures the idea that the heat, or enthalpy change, of a given process can be expressed as the sum of the heats of several other processes that, when combined, yield the process of interest.