Hess's Law

[kiara chan]

During friday's class, we went over three different methods on calculating enthalpy change. I know that the third method using the sums of product minus initial isn't as specific, but which of the other 2 methods would be most preferred?

[Neelaj Das 3I]

I don't think there is particularly any method that is "preferred". You should know each method and when to use it based on a given problem. Sometimes, you may be given the bond enthalpy information meaning you have to use the second method, etc. It's all situationally based on the problem and the information provided.

[Caitlin_Tang_Dis3H]

I agree with Neelaj. Based on what the professor went over in class, we can use Hess's Method when we have 2 reactions that we can add to get a net reaction and thus a net change in enthalpy. With method 2, we can use bond enthalpies to calculate the enthalpy change with one reaction given. And the third method, like Kiara stated, can be used when we have combustion involved.

[Kathryn Heinemeier 3H]

I think it'll mostly just depend on what information we're given in the problem.

[Lesley Kim 1K]

All the different methods can be used to solve questions about enthalpy changes. The method you choose is going to be the one you find the most convenient based on the information provided!

[Kaira Shibata 1E]

Neither is preferred, it really just depends on what information is given in the question. Whichever set is given, you do the corresponding calculations.

[Veronica Larson- 1I]

I think it just depends on what information we are given. For example, if you are given the bond enthalpies in the question, it would be the most convenient to use the second method, but that doesn't mean it will necessarily work for every question so you just have to decide based on what you're given. Hope that helps!

[Arya Bhalla 1H]

The method used depends on which information is given. Is you are given bond enthalpies, then you can use this information to draw out the compounds and figure out which bonds are broken and formed.

[Kainath Kamil Dis 2K]

It depends on what information you are given in the problem. like whether you've been given bond angle, etc.

[joshua_quinn_1C]

The method you would use depends on the information given in the problem and what it is asking for. Hope this helps!

[Allen Mayo 1E]

I believe each method is useful based on what is the given for the problem. There is not a "preferred" method.

[Om Patel]

it does not matter what method you choose

[Hannah Thornton 1F]

No method is specifically preferred, it just depends on what information is given in the question.

[805401611]

From my understanding, I believe the method used is based off the problem that is given to you, not so much that there is a preferred method. It's problem by problem

[Kimberly_martinez2I]

As people have previously said, I don't think any method is preferred. Knowing all the methods would be more helpful because ultimately it depends on the information given in the question.

[Cynthia_L_2C]

There is no preferred method. For these, you just go based on the problem.

[raynebunado]

I think you pick the method that works best with what you're given in the problem!

[kayleec1004]

There is no "preferred" method. It depends on the information given in the problem.

[Reece Fong 2k]

The best method is the method you can use with the information given to you.

[Hannah_Pon_1F]

Like what everyone said choose the method according to the information you are given but also usually it's "easier" to add and subtract the reaction enthalpies compared to calculating all of the energies for bonds being broken and formed.

[Alexander Moroz 1B]

The information given in a problem guides you in choosing the best method for determining emt happy or reactions. If the problem gives you several reactions and each of their heat of reactions then use Hess’s law, if you are given bond enthalpies, use bond enthalpies, etc.