Question

In the reaction, 2ch4(g)⟶c2h4(g) 2h2(g) , if the enthalpy change cannot be directly measured, which principle allows us to calculate it using Hess's Law?

a. Conservation of Energy
b. Avogadro's Principle
c. Boyle's Law
d. Dalton's Law

Answer 1

Hess's Law, which relies on the Conservation of Energy, enables us to calculate the enthalpy change for a reaction by summing the enthalpy changes of individual steps comprising the overall process.

Step-by-step explanation:

The principle that allows us to calculate the enthalpy change for the chemical reaction 2CH4(g) → C2H4(g) + 2H2(g), when it cannot be directly measured, is the Conservation of Energy as stated in Hess's Law. Hess's Law explains that if a process can be expressed as the sum of several stepwise processes, the enthalpy change for the entire process will be the sum of the enthalpy changes for the individual steps. This law is applicable because enthalpy is a state function, meaning that its change depends only on the initial and final states of the process and not on the path taken. Therefore, we can use known enthalpy changes of other reactions to find the enthalpy change for a reaction of interest.