difference between enthalpy and internal energy

[tammie123]

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U = q + w
H= U + PV

I don't understand this isn't isn't PV the work of expansion term, so isn't this the same as w? So why is it added onto U in the second equation?

Also my lecture slides say: 'dU = dw + dq
=-pexdV + dq'

Why is the pexdV term minus? Since w = p△V, so shouldn't it be added on not taken away since in the first line dw is added on?

 

[87asu]

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[87asu]

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[tammie123]

1.) Enthalpy accounts for all of the energy of the system, which is why the internal energy is added to PV. Enthalpy is not calculated, but a change in enthalpy is.

2.) the negative sign associated with the external pressure x change in volume is indicating that work is being done by the system onto the environment. It is better to under stand that work done by the system is a loss of energy, and that work done onto the system is energy input rather than memorize a positive/negative formula.

Yes but if you substitute the equation for U into the one for H you get H= w + q + PV, and since w=pv if the substitute that in the equation becomes: H = PV + q + PV. Why are we adding PV twice?! Do you understand where my confusion is coming from.

What exactly is the difference between work and work of expansion, and enthalpy and internal energy?

 

[tammie123]

also khan academy has a ton of helpful easy to understand videos covering thermodynamics that helped me through pchem, I suggest you check them out.

Or maybe the work refers to all types of work not just work of expansion and so therefore the work is not always equal to PV so this equation is not always the case w = PV, that would make ALOT more sense to me.

 

[87asu]

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[87asu]

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[oldstock]

Also can I ask if this class is being taught as a part of pharmacy school, or your undergrad? I'm only wondering as you are listed as a pharmacy student, and it will be good to know that i'm entering with a strong background if that's the case.

The OP is probably in the "pre-pharm" phase of a 5 or 6 year pharmacy program as I was talking to several pharmacists and none of them told me P-Chem or things like this stuff discussed here being taught in the "professional phase".

you do have a strong background from what I am seeing here. Excellent !! 👍👍

 

[87asu]

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[tammie123]

The OP is probably in the "pre-pharm" phase of a 5 or 6 year pharmacy program as I was talking to several pharmacists and none of them told me P-Chem or things like this stuff discussed here being taught in the "professional phase".

you do have a strong background from what I am seeing here. Excellent !! 👍👍

Also can I ask if this class is being taught as a part of pharmacy school, or your undergrad? I'm only wondering as you are listed as a pharmacy student, and it will be good to know that i'm entering with a strong background if that's the case.

I watched a few khan academy videos and it actually helped a fair bit, hopefully after watching a few more I'll fully understand it.

By the way, I'm a first year pharmacy student in England and over here we don't have to do another degree before pharmacy. They basically teach us all the basics in the first year and we haven't started learning the 'professional' stuff yet. So this probably explains it.

 

[ramizlol]

I watched a few khan academy videos and it actually helped a fair bit, hopefully after watching a few more I'll fully understand it.

By the way, I'm a first year pharmacy student in England and over here we don't have to do another degree before pharmacy. They basically teach us all the basics in the first year and we haven't started learning the 'professional' stuff yet. So this probably explains it.

I knoq this is off topic but how is market for pharmacists in the UK?

 

[tammie123]

I knoq this is off topic but how is market for pharmacists in the UK?

I'm not going to lie, it's getting more and more difficult for graduates to get jobs due to more and more pharmacy schools opening in the UK and the employment rates are pretty low (it's around 60%), but luckily I'm going to a very well respected pharmacy school so if I can get through the next few years and get a degree from here then it should be a little easier. For my university the employment rate is 97%. So it depends on where you get your degree from.

Are you thinking of moving to the UK?

 

[ramizlol]

I'm not going to lie, it's getting more and more difficult for graduates to get jobs due to more and more pharmacy schools opening in the UK and the employment rates are pretty low (it's around 60%), but luckily I'm going to a very well respected pharmacy school so if I can get through the next few years and get a degree from here then it should be a little easier. For my university the employment rate is 97%. So it depends on where you get your degree from.

Are you thinking of moving to the UK?

I would love to but it wont be worht it finanically. I will have to pay US and UK taxes :/

 

[oldstock]

I'm not going to lie, it's getting more and more difficult for graduates to get jobs due to more and more pharmacy schools opening in the UK and the employment rates are pretty low (it's around 60%), but luckily I'm going to a very well respected pharmacy school so if I can get through the next few years and get a degree from here then it should be a little easier. For my university the employment rate is 97%. So it depends on where you get your degree from.

Are you thinking of moving to the UK?

I think you guys should get together and petition the Queen. Her Majesty could shut down all the for-profit schools, not like here in the US where we claim we are a "free market" and a "democracy".