delta U= delta H


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Emily Vainberg 1D
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delta U= delta H

Postby Emily Vainberg 1D » Mon Feb 10, 2020 3:06 pm

When does the Internal Energy (delta U) = delta H?

Jessica Castellanos
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Re: delta U= delta H

Postby Jessica Castellanos » Mon Feb 10, 2020 3:23 pm

I think, at constant volume and constant pressure, delta U is equal to delta H.

Dina Marchenko 2J
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Re: delta U= delta H

Postby Dina Marchenko 2J » Sat Feb 15, 2020 6:08 pm

When there is a constant volume or pressure, no expansion or compression work is being done by the system so w=0. When heat is at constant pressure, it equals the enthalpy change, so at constant pressure, delta U is equal to delta H.

Rebekah Alfred 1J
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Re: delta U= delta H

Postby Rebekah Alfred 1J » Sat Feb 15, 2020 7:23 pm

When the volume of the reactants is equal to the volume of the products, delta U is equal to delta H.

Kayla Maldonado 1C
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Re: delta U= delta H

Postby Kayla Maldonado 1C » Sun Feb 16, 2020 3:32 am

Delta U= q+w and under constant pressure, qp=delta H and when no work is done Delta U=Delta H

Leonardo Le Merle 1D
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Re: delta U= delta H

Postby Leonardo Le Merle 1D » Thu Mar 12, 2020 11:52 am

The answers to this question
viewtopic.php?t=25381
Were also pretty helpful for me sorting it out in my head, hope they help!

Jacob Motawakel
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Re: delta U= delta H

Postby Jacob Motawakel » Thu Mar 12, 2020 2:08 pm

under constant volume delta U equals delta H because at constant pressure q equals H and at constant volume no work is being done, so in that case U=q which is U=H in contact pressure and volume.

Frankie Mele 3J
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Re: delta U= delta H

Postby Frankie Mele 3J » Mon Feb 01, 2021 1:17 pm

The standard equation deltaU=deltaH - P*deltaV accounts for any change in the volume, however, when delta V = 0, the equation changes to deltaU=deltaH - P*0. This is when deltaU=deltaH because P*0 will not affect the internal energy (delta U).

arisawaters2D
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Re: delta U= delta H

Postby arisawaters2D » Wed Feb 03, 2021 11:31 am

Just to clarify, delta U=delta H when pressure and volume are constant and no work is being done?

SamanthaTolentino 3D
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Re: delta U= delta H

Postby SamanthaTolentino 3D » Wed Feb 03, 2021 11:52 am

arisawaters2D wrote:Just to clarify, delta U=delta H when pressure and volume are constant and no work is being done?

yeah if we have constant volume, delta U is equal to qv and when we have constant pressure delta U is equal to qp. As a result we have delta U = delta H - PdeltaV. However, if P and V are constant then we just have delta U=delta H

Tanya Nguyen 1B
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Re: delta U= delta H

Postby Tanya Nguyen 1B » Thu Feb 04, 2021 10:16 pm

SamanthaTolentino 3D wrote:
arisawaters2D wrote:Just to clarify, delta U=delta H when pressure and volume are constant and no work is being done?

yeah if we have constant volume, delta U is equal to qv and when we have constant pressure delta U is equal to qp. As a result we have delta U = delta H - PdeltaV. However, if P and V are constant then we just have delta U=delta H

So substituting delta U = q + w, how is q equal to delta H when pressure is constant?

Ximeng Guo 2K
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Re: delta U= delta H

Postby Ximeng Guo 2K » Fri Feb 05, 2021 5:13 am

When there is no change in volume, there is no delta w, delta U = delta H

Rahul Sobti 1E
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Re: delta U= delta H

Postby Rahul Sobti 1E » Fri Feb 05, 2021 10:13 am

When there is constant pressure on no work done by expansion the DeltaU = DeltaH

Jason Knight - 1F
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Re: delta U= delta H

Postby Jason Knight - 1F » Fri Feb 05, 2021 10:27 am

Delta U is equal to delta H when there is no change in volume, so that means that work equals zero. This is because no expansion or compression is done, and work equals zero.

Brandon Le 3C
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Re: delta U= delta H

Postby Brandon Le 3C » Fri Feb 05, 2021 4:32 pm

We can only say that delta U = delta H when there is no work done on the system. This means that there will be no change in volume and no change in pressure.

Madeline Louie 1B
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Re: delta U= delta H

Postby Madeline Louie 1B » Fri Feb 05, 2021 4:43 pm

When there is constant pressure and a constant volume, delta U is equal to delta H.

Sofia Lombardo 2C
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Re: delta U= delta H

Postby Sofia Lombardo 2C » Fri Feb 05, 2021 10:49 pm

when there is no work (work = 0). This occurs when there is constant volume (since the work equation =.

Jiapeng Han 1C
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Re: delta U= delta H

Postby Jiapeng Han 1C » Sat Feb 06, 2021 7:13 pm

When there is no work done. In other words, delta U=delta H when there is no change in volume, ex. in an ideal gas.

emwoodc
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Re: delta U= delta H

Postby emwoodc » Sun Feb 07, 2021 11:28 pm

This means that when there is constant pressure AND constant volume, delta H (enthalpy) equals delta U

Joshua_Chan_3K
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Re: delta U= delta H

Postby Joshua_Chan_3K » Sun Feb 07, 2021 11:46 pm

The easy way to remember this is that work is equal to force times distance. Distance in our case is when a plunger or something similar is usually pushed into the chamber or out of the chamber which changes the volume. Therefore when their is no change in volume, work = 0. Once work = 0 the only thing left in the equation is delta U = change in enthalpy.

Elizabeth Kaplan 3I
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Re: delta U= delta H

Postby Elizabeth Kaplan 3I » Mon Feb 08, 2021 12:28 am

Internal energy equals change in enthalpy at constant pressure and volume. This is because internal energy equals q (heat) at constant volume (since the system is not doing any work), and q equals delta H at constant pressure.

Hasan Mirza 3F
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Re: delta U= delta H

Postby Hasan Mirza 3F » Mon Feb 08, 2021 12:32 am

As long as Pressure and Volume are constant, they are equal because no work is being done.


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