Hess Law

[Cecilia Lei 3K]

Can someone please explain Hess Law more in detail? I think I didn't quite get that.

[Jaden Nguyen 2A]

It's important to remember that Hess' Law works because enthalpy is a state function. You can add change in enthalpies together to obtain the total enthalpy of the entire reaction. If you remember, we added equations with acids and bases where we needed to change the Ka or Kb value depending on what we did to the reactions. Hess' Law is the exact same thing but there are some rules you have to follow, which you can find in the textbook. You can manipulate the equations so they add up to the final equation by multiplying the stoichiometric coefficients or flipping the equation in reverse. Hope this helps!

[Morgan Oey-3H]

Basically, Hess’s law states that you can add the enthalpy change of reactions together to find the total enthalpy change of a reaction. It’s basically addition, adding up enthalpies (that the book or question will give you) and seeing if the Net change is positive (endothermic) or negative (exergonic).

[Daniel Li 3C]

In simple terms, Hess's Law uses the fact that enthalpy is a state function. It shows that you can add and reverse equations when trying to find the total change in enthalpy for an overall equation.

[Meghan Terrell 1B]

Since enthalpy is a state function, we can add the enthalpy of multiple steps together to find the overall enthalpy of a reaction. So when given a Hess's Law problem, there is most likely a few different reactions with individual enthalpies and you are asked to find the enthalpy of a given reaction. Basically, you want to combine the given reaction steps in a way that cancels out intermediates to give you the overall reaction you are looking for. For instance, you may need to multiply one of the steps by a coefficient, and you would multiply its corresponding enthalpy by the coefficient. You may need to flip a reaction, in which case the enthalpy switches signs. You may also not use one of the given equations at all. Once you have used the equations to create the overall reaction, you can add the manipulated enthalpies together to get the overall enthalpy. This concept is kind of like when we did K values for reactions and would combine multiple reactions together to find the K of an overall equation (but remember the manipulation of K is different than here for enthalpy).

[Michelle_Duong_3H]

Hello,

Hess's Law states that enthalpy changes are additive. This is possible because enthalpy is a state property, in which the value is determined by the current state, independent of the path taken to obtain that state. Thus, when calculating total enthalpy of a reaction, we can add, subtract, and/or multiply the enthalpies of the reactions that make up that final reaction.

Hope this helps!

[Amanda Pineda 3H]

Hess's law is a variation of the first law of thermodynamics and it basically says that the energy change in an overall chemical reaction is equal to the sum of the energy changes in the individual reactions comprising it. Hope this helps!

[Arjan G 2H]

Hi! Hess' Law basically states that energy change in the overall reaction is the sum of the energy changes in each reaction that makes it up. This essentially means that we can measure the net change of a reaction by adding the enthalpy or energy changes of each reaction that makes sit up. Usually, these individual changes are given to us, and we have to adjust them in order to equate them to the intended final result we want. Then, we add these changes in energy to get our final answer. I hope this helps!

[Aashna Bhandari 1L]

Due to the fact the enthalpy is a state function, we can use Hess's Law which states that the energy change in an overall chemical reaction is equal to the sum of the energy changes in the individual reactions comprising it. This means we can manipulate known reactions and their enthalpies in order to sum them up to the reaction and the enthalpy we are trying to solve for.

[Hailey Sarmiento 3E]

Hess's law is useful when you are given the enthalpies of multiple "mini" reactions that essentially make up the bigger reaction you are trying to find enthalpy of. Since enthalpy is a state function, you can take the sum of all "mini" enthalpies to get the overall or net enthalpy. to make sure you have the right sign for each "mini" enthalpy, though, you should check the final reactants and products and make sure that the partial reactions have the same reactants and products when combined. Some reactants and products may cancel each other out which is why they may not be shown in the overall reaction. if you do end up reversing a reaction, so it makes sense for the overall reaction, you need to switch the sign of the enthalpy for that reaction.

[Audrey Banzali-Marks 1A]

Hess's law is using the fact that enthalpy is a state property (it doesn't depend on the pathway, just the current state) to justify adding up enthalpies for steps of a reaction in order to get the total enthalpy of the whole reaction.

[Kathleen Wijaya 3L]

In a multi-step reaction, to get the net reaction energy we can add together the individual reactions' energy values.

[trevina_brown_2A]

Hess's Law shows that you can add and reverse equations when trying to find the total change in enthalpy for an overall equation.

[Nicole Weinstein 3E]

Since Hess's Law is a state function (meaning it doesn't matter how many steps it takes to get to the final value) you can take given reaction equations and their enthalpies to add, reverse, multiply, and cancel out to try and match it to the desired reaction. You do this by manipulating the given enthalpies to find the value of the required reaction's enthalpy.

[Abigail Tran 14a]

You use Hess's law to find total bond enthalpies, enthalpies of reactions or products, and to calculate heat of formation, combustion neutralizations, ionization, etc...It is basically like adding all of the enthalpies in order to find total enthalpy. If you multiply an equation by n, you have to raise k to the power of n. If you use the reverse of an equation, you do 1/k. If you add add equations you do ka x kb.

[Divya Mehta 2K]

Hess's law is essentially a variation of the first law of thermodynamics, claiming that the change in energy in an overall chemical reaction equals the sum of the energy changes in individual reactions that make it up.

[elliemehrara]

Hess's Law works off of the fact that enthalpy is a state function, meaning the change in enthalpy is not dependent on the path taken to make that change. This means that the total enthalpy of a reaction is equal to the sum of all the enthalpy changes of the reactions that comprise it.

[Rebekah Jung 1C]

Hess's Law states that enthalpy works as a state property. This will allow for us to calculate the total enthalpy by adding the enthalpies of the steps that compose it.

[Grant_2A]

Hesses law uses that fact that enthalpy is a state function and states that you can add and reverse equations and their enthalpies to find the total enthalpy of a system.

[Mahli Martinez 2I]

In sum, Hess's Law states that the change in energy in an overall chemical reaction is equal to the sum of the energy changes in the reactions that compromise the overall reaction. With this law, we are able to add the enthalpies of said reactions to calculate the total enthalpy of the system (and do the reverse calculation as well).

[205484435]

Hess's Law uses the idea that enthalpy is a state function which says that it is additive so you can add to find the total change in enthalpy for an overall equation.

[Matthew Vu 3C]

Hess's law allows us to add, reverse, and multiply/divide equations and their enthalpies to find the total enthalpy of a system.

[Collin Le 3I]

Hess' Law allows us to find the enthalpy change of a reaction if we are given the enthalpy changes of reactions that make up the reactants and products of the reaction we are investigated. This process includes adding the enthalpy change of multiple reactions together.

[SofiaMammaro-1K]

Hess's Law states that: “The total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions are the same.”

[Kayla Ziebell 1H]

It basically says that because enthalpy is a state property, enthalpies can be added to find a total value for enthalpy. By manipulating different reaction equations, one can find the total enthalpy of a reaction through addition using Hess' law.

[Sarthika Chimmula 3H]

Hess's Law is based on the fact that enthalpy is a state function and therefore has additive properties. This means that you can add up the enthalpy changes of multiple smaller equations to find the total enthalpy change from your beginning reactants to the final product.

[SuryaDham 3E]

hess's law allows you to add the enthalpies for the pathways of a reaction to achieve the overall enthalpy for the reaction, it uses the property of state function to do so.

[Caitlyn Lo 2F]

Hess's law states that you can add the enthalpies that coincide with the pathways of the reaction in order to get the overall enthalpy

[Rebecca Preusch 2C]

It basically says that a chemical reactions, delta H is the sum of the delta H of the simpler reactions that make up the overall reaction.