True or False: Hess's Law indicates that if there is an alternate path to run a chemical reaction, say in a series of steps, the change in enthalpy for that reaction will be the sum of the changes in enthalpy for the steps.
The question is not clear to me. Which sum? The sum of all steps, including the alternate steps or something else?
Hess's law was only used to calculate heat change of phase transitions
True. Hess's Law states that if a chemical reaction can be expressed as the sum of several steps, then the overall change in enthalpy for the reaction is equal to the sum of the enthalpy changes for each individual step. This principle is based on the fact that enthalpy is a state function and is independent of the pathway taken. Thus, regardless of the specific steps or intermediates involved in a reaction, the net change in enthalpy will be the same.
To determine the change in enthalpy for a reaction, you can follow these steps:
1. Identify the individual steps or reactions that can be used to describe the overall reaction.
2. Find the enthalpy change for each individual step. This can be done experimentally by measuring the heat evolved or absorbed during each step, or through theoretical calculations using thermochemical equations or tables.
3. If necessary, balance the equations for each step to ensure the stoichiometric coefficients match the overall reaction.
4. Use the principle of Hess's Law to find the overall change in enthalpy by summing up the enthalpy changes of the individual steps.
By applying Hess's Law, it becomes possible to determine the enthalpy change for a reaction indirectly, even if it is difficult or impractical to measure it directly.