## 3 methods for enthalpy calculation

Deepika Pugalenthi 1A
Posts: 60
Joined: Fri Sep 28, 2018 12:24 am

### 3 methods for enthalpy calculation

In class, Professor Lavelle taught three ways to calculate enthalpy. Which method is the most effective and during a test will be told which method to use?

Calvin Patel 2H
Posts: 37
Joined: Fri Sep 28, 2018 12:22 am

### Re: 3 methods for enthalpy calculation

Usually you would want to use either the enthalpy of formation or of combustion methods. These are the most accurate and easiest to use. Using the mean bond enthalpy is less accurate and it can get confusing at times. It really depends on what equations you are given and what values you know. There is no "easiest" way. It all just depends.

Posts: 62
Joined: Fri Sep 28, 2018 12:23 am

### Re: 3 methods for enthalpy calculation

I'm not exactly sure which method we will be asked to do although I do know that using bond enthalpies to find delta H is not as accurate. So try to stay away from that one if looking for a more precise answer. I have a feeling we are going to be prompted to solve the problem in a certain way so just be prepared for anything!

michelle
Posts: 62
Joined: Fri Sep 28, 2018 12:23 am

### Re: 3 methods for enthalpy calculation

Our TA says you just need to examine the giver conditions to choose methods. But definitely remember using bond enthalpy is the least accurate.

LilyL1C
Posts: 24
Joined: Fri Sep 28, 2018 12:20 am

### Re: 3 methods for enthalpy calculation

It really depends on the given conditions in the question. If they give you the values for bond enthalpy, use bond enthalpy; if they give you the values for combustion, use combustion, etc. But keep in mind that bond enthalpy is the least accurate because those values are averages.

Henry Dudley 1G
Posts: 61
Joined: Fri Sep 28, 2018 12:16 am

### Re: 3 methods for enthalpy calculation

Calvin Patel 2H wrote:Usually you would want to use either the enthalpy of formation or of combustion methods. These are the most accurate and easiest to use. Using the mean bond enthalpy is less accurate and it can get confusing at times. It really depends on what equations you are given and what values you know. There is no "easiest" way. It all just depends.

Of enthalpy of formation vs. combustion, which of these two would be the most accurate?

Calvin Patel 2H
Posts: 37
Joined: Fri Sep 28, 2018 12:22 am

### Re: 3 methods for enthalpy calculation

Henry Dudley 1G wrote:
Calvin Patel 2H wrote:Usually you would want to use either the enthalpy of formation or of combustion methods. These are the most accurate and easiest to use. Using the mean bond enthalpy is less accurate and it can get confusing at times. It really depends on what equations you are given and what values you know. There is no "easiest" way. It all just depends.

Of enthalpy of formation vs. combustion, which of these two would be the most accurate?

They are both very accurate. I do not think either one is more accurate than the other. It's more of which method is more convenient to use at the moment.

Jacob Bershatski 4C
Posts: 30
Joined: Fri Sep 28, 2018 12:21 am

### Re: 3 methods for enthalpy calculation

I think on the test he will tell us which method to use. However, he did mention in class that using bond enthalpy is the least accurate means of calculation the enthalpy of the reaction. This is because, aside from diatomic molecules like Cl2, the bond enthalpies given are averages rather than exact values.

Katelyn Phan 2A
Posts: 61
Joined: Fri Sep 28, 2018 12:23 am

### Re: 3 methods for enthalpy calculation

The most effective method would be based on the conditions given. The only difference is the accuracy and reliance of the method.

Posts: 47
Joined: Fri Sep 28, 2018 12:15 am

### Re: 3 methods for enthalpy calculation

What are the three methods for enthalpy calculation in order from least to most accurate?

deepto_mizan1H
Posts: 65
Joined: Fri Sep 28, 2018 12:16 am

### Re: 3 methods for enthalpy calculation

If we are given the actual steps for each part of the reaction, then that is the most accurate way to find the enthalpy for the reaction (Hess's Law). Then, from the enthalpies of formation we would be able to get another method of finding the total enthalpy, but it would not be as accurate since it doesn't follow the exact reaction. Lastly, if we calculate the enthalpy using bond enthalpies (an average enthalpy for each bond) it would be even less accurate. On the test, it will be evident from what we have to do based off of if we are given the steps, or formation, or bond enthalpy.