Hess's Law

[905771517]

Hi, I am still confused about how Hess's Law is used to determine the enthalpy change of a reaction, could somebody please help?

[Maia Hull 1H]

Hess's law is what allows you to simply add the enthalpy values of other reactions to come up with the enthalpy value for the desired reaction. For example, if you need to combine two chemical equations to form the desired reaction, then to find the total enthalpy change, you would add the enthalpy values of both the reactions.

[Nikta Seyedin 3D]

Hello,
In order to help you understand the Hess’s Law better as a way to determine the enthalpy change of a reaction, I will explain it step by step. First, whenever you are given a series of reactions, and are told to find the enthalpy of the net reaction, you will utilize the Hess’s Law method. The way you will do it is that you will find your net reaction based on the component steps that have a known enthalpy values. Then, in order to find the enthalpy change you will add all the enthalpy changes for the steps of the reaction.

[Zain Syed 1E]

Hess's law is used to determine the enthalpy of reaction when you have two or more reactions and want to combine them. When you do this, you can add the deltaH of each reaction to get the net deltaH.

[Eli Weiss-Hung 2C]

Hello, Hess's law is used when you are given the enthalpy changes for multiple reactions that can then be combined to form some other reaction (that the enthalpy change is not given for). The reactions can be added together with intermediate products and reactants cancelling each other out so that only the initial reactants and final products remain, and the enthalpy changes are also added together. If a multiple of one reaction is needed to add to another reaction, the enthalpy change for that reaction most be multiplied by the same number.

[Phanuphong Techasiri]

Hess's Law is used to determine the enthalpy change of a reaction that cannot be directly measured by combining the reactants and measuring the heat evolved or absorbed. Instead, the enthalpy change of the reaction can be calculated by adding up the enthalpy changes of a series of reactions whose sum is the desired reaction.

[Kush Brahmbhatt 2K]

Hess's law essentially helps find the overall enthalpy of multiple reactions together. This can be done by taking the series of equations, adjusting them as to cancel out intermediate reactants and respectively adjusting the individual enthalpies, and adding them all together.

[AChassion Dis2A]

Hess's Law allows you to add up reactions to get a final enthalpy.

It's kind of like when we were trying to find the new equilibrium constants for larger reactions when given a bunch of equilibrium constants for smaller ones. We had to toy around with the equations we had to form our final equation and cancel things out. Instead of multiply each of the steps' K's, we are adding up the individual steps' enthalpy.

Hope that helps.

[Hoang Nguyen 3H]

Hi, just add the enthalpy of each state change to get the total enthalpy change.

[Kylie Cheng 1G]

Hess's Law means that you can add up the enthalpies at each state to get the total enthalpy change. If you've taken calculus, think of it like the integral (where he made the integral symbol into the word "sum").

[jhb123]

Hess's Law simply states that, in order to calculate the enthalpy of a reaction, you can add (or "couple) the enthalpies of related reactions. Put in simpler terms, if a process can be expressed by the sum of two or more steps, the enthalpy change is the sum of the delta(H) value for each of the steps. It is, in context, the NET ENTHALPY of the related reactions.

[eriko vong 3D]

Hess's Law just states that you can calculate the overall enthalpy change of a reaction by adding together the enthalpy values for each state.

[Anabelle Pham 2C]

With Hess's law, you can basically just add up all of the enthalpies of each state change to get the overall change in enthalpy.

[305943084]

If you can combine multiple reactions into one single reaction, than the final reaction enthalpy would just be the sum of all the reaction enthalpies of the individual reactions.

[sherwin arian 1K]

Hess's Law basically means that the total enthalpy for a reaction you're trying to find is just the sum of all the enthalpies of a set of reactions that equals the reaction you are trying to find.

[Viviana Hsiao 1G]

You use Hess' Law to calculate the total change in enthalpy of given reactions. You are basically trying to find the "wanted" reaction based on the given reactions by adding, multiplying, or flipping the reactions. When you do anything to the reaction, you also do the same to the enthalpy. At the end, you add up the total change in enthalpy of the reactions.

[Sunny Do 1G]

Hess's Law allows you to add the enthalpies of multiple given reactions to find the total enthalpy. You can arrange the reactions to fit a wanted reaction by reciprocating or multiplying them by a constant. Doing that would also affect the enthalpy and you would multiply by -1 if you are using a reverse reaction or multiplying by a constant.

[Daniel Nguyen 2L]

Hess's Law simply states that the total enthalpy change for a reaction is the sum of the enthalpy changes of each step. If you can add two reactions, you can obtain the net change, also known as the ΔH value.

[Sabrina Camua 2J]

Hess’s law states that the sum of all enthalpies in a set of reactions is equal to the reaction’s overall enthalpy. So, you’re able to get the total enthalpy change by adding up all of the enthalpies of each state change.

[Katherine Phan 1J]

Hess's Law is a result of the fact that enthalpy is a state function. The enthalpy for a reaction is equal to the total of the enthalpies for each of the individual steps/reactions that are added to get that reaction. You can also manipulate each thermochemical equation by multiplying by coefficients or reversing them, in which case, the enthalpy would also be multiplied by the coefficient or -1. In the end, after adding all the steps to get the desired reaction, you would also add their respective enthalpies to obtain the total enthalpy.