## Standard enthalpies of formation

Minh Ngo 4G
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### Standard enthalpies of formation

Hi, for questions such as 4D.9, are we supposed to Google the delta H for each compound?? I can't seem to find any table or something like that in the book? Is that the case for all the other problems that want us to find deltaH too?

Ryan Chang 1C
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### Re: Standard enthalpies of formation

I google the enthalpies of formation because not all of them are given in the textbook. I'm sure if a test like this ever appear on an exam Prof. Lavelle would provide us with a table of enthalpies of formation.

Angus Wu_4G
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### Re: Standard enthalpies of formation

You only need to find the enthalpy of formation for carbon dioxide and water. The enthalpy of formation for oxygen and nitrogen gas is zero.

gconcha
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### Re: Standard enthalpies of formation

I highly doubt that we'll be required to memorize enthalpies of formation, so I assume they'll be given on a test. This would be a good question for Dr. Lavelle himself.
Remember which ones can be cancelled because they're in their base state, though. You might have to memorize those, but I believe knowing of noble gases and diatomic halogens is enough to get by.

Sofia Barker 2C
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Joined: Wed Sep 18, 2019 12:21 am

### Re: Standard enthalpies of formation

I think that those values will be provided on tests and such, but make sure to remember that the standard enthalpy of formation for elements in their most stable form is 0. So pay attention to the phases that certain elements are in because that will indicate whether or not you should look up the value or use 0.

Minh Ngo 4G
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### Re: Standard enthalpies of formation

gconcha wrote:I highly doubt that we'll be required to memorize enthalpies of formation, so I assume they'll be given on a test. This would be a good question for Dr. Lavelle himself.
Remember which ones can be cancelled because they're in their base state, though. You might have to memorize those, but I believe knowing of noble gases and diatomic halogens is enough to get by.

Hi, what does base state mean? I know that if it is a solid let’s say, we have to find enthalpy for its from solid to liquid and then to gas? Is that what it is called

Amy Pham 1D
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Joined: Fri Aug 09, 2019 12:15 am

### Re: Standard enthalpies of formation

Minh Ngo 4G wrote:
gconcha wrote:I highly doubt that we'll be required to memorize enthalpies of formation, so I assume they'll be given on a test. This would be a good question for Dr. Lavelle himself.
Remember which ones can be cancelled because they're in their base state, though. You might have to memorize those, but I believe knowing of noble gases and diatomic halogens is enough to get by.

Hi, what does base state mean? I know that if it is a solid let’s say, we have to find enthalpy for its from solid to liquid and then to gas? Is that what it is called

In this case, base state is likely referring to molecules in the most stable state in which their enthalpies of formation are equal to zero, and thus can be disregarded in calculating the total enthalpy of reactions when using Method 3, standard enthalpies of formation.

gconcha
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### Re: Standard enthalpies of formation

Minh Ngo 4G wrote:
gconcha wrote:I highly doubt that we'll be required to memorize enthalpies of formation, so I assume they'll be given on a test. This would be a good question for Dr. Lavelle himself.
Remember which ones can be cancelled because they're in their base state, though. You might have to memorize those, but I believe knowing of noble gases and diatomic halogens is enough to get by.

Hi, what does base state mean? I know that if it is a solid let’s say, we have to find enthalpy for its from solid to liquid and then to gas? Is that what it is called

Things such as oxygen gas ($O_{2}$) quite like to be in their state, and making it into monotomic oxygen ($O$), ozone ($O_{3}$) or otherwise is a process that not only requires extra energy (which can be measured through enthalpy) but will fundamentally create a scenario in which that new compound will always be trying to go back to its more stable, original state of $O_{2}$ . Because $O_{2}$ is the most stable form here, we can assume that no energy was required to bring it there, so its enthalpy of formation is technically negative, but we'll just assume zero.

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