Expansion work

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Alex Tchekanov Dis 2k
Posts: 118
Joined: Sat Aug 24, 2019 12:16 am

Expansion work

Postby Alex Tchekanov Dis 2k » Mon Jan 27, 2020 3:50 pm

When you are calculating the difference of energy used to raise the temperature, why does the expansion of the volume change the amount of heat change?

Brian_Ho_2B
Posts: 221
Joined: Fri Aug 09, 2019 12:16 am

Re: Expansion work

Postby Brian_Ho_2B » Mon Jan 27, 2020 4:07 pm

Alex Tchekanov Dis 2k wrote:When you are calculating the difference of energy used to raise the temperature, why does the expansion of the volume change the amount of heat change?


Calculating the difference in energy used to raise temperature depends on which variables are constant. If we are talking about a gas, then a gas's heat transfer can be calculated using q_v or q_p (the underscore represents my futile attempt of writing a subscript). q_v is the heat equation for constant volume, and it's calculated via the equation q_v = n(C_m,v)(delta temperature).
For constant pressure, q_p is calculated via the equation q_p = n(C_m,p)(delta temperature). The C values for constant pressure and constant temperature are different, with the C value for constant pressure typically higher.

Ruby Tang 2J
Posts: 102
Joined: Fri Aug 30, 2019 12:15 am

Re: Expansion work

Postby Ruby Tang 2J » Mon Jan 27, 2020 4:10 pm

When heat is added at constant volume, all of the heat is used to increase the temperature of the substance. However, when heat is added at constant pressure, the volume is changing and therefore more heat is needed to achieve the same temperature when volume is constant. This is because not only is the heat contributing to increasing the temperature of the substance, but it is also used to do the work required to expand the gas. The gas cannot expand on its own; it must consume energy.


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