how does II work out? why should heat flow change based on path taken?
i think just maybe that i hate thermodynamics more than buffers! it's like falling in love all over again..
heat flow
- Thread starter chiddler
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how does II work out? why should heat flow change based on path taken?
i think just maybe that i hate thermodynamics more than buffers! it's like falling in love all over again..
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1. Isothermal expansion
2. Isovolumetric heating followed by isobaric expansion
3. I don't know what this is to be honest.
I. You can use the first law of thermodynamics to solve for the work done on or by the system in each case. (Or simply calculate the area under each curve as in the second figure)
II. Remember heat transfer is a process (or path) function, as opposed to a state function. Heat (or enthalpy) is the sum of the internal energy of a thermodynamic state and the work required to get there. Looking at the equation for enthalpy, you'll see that if two states (PV) are equal and their internal energies (U) are different (because the work done to get to each state is different) then it follows that there must be an enthalpy change in doing so.
III. You can use the fundamental thermodynamic relation to solve for the difference in internal energy between both states.
IV. This one's the easiest. Assuming no mass is lost: n is constant, R is constant, you know the Ps and Vs, solve for delta(T) for each case (using the ideal gas law).
*Disclaimer - I'm very rusty with my thermo so all of this might be completely wrong and I defer all liability to Bush/Obama (depending on your political preference).
2. Isovolumetric heating followed by isobaric expansion
3. I don't know what this is to be honest.
I. You can use the first law of thermodynamics to solve for the work done on or by the system in each case. (Or simply calculate the area under each curve as in the second figure)
II. Remember heat transfer is a process (or path) function, as opposed to a state function. Heat (or enthalpy) is the sum of the internal energy of a thermodynamic state and the work required to get there. Looking at the equation for enthalpy, you'll see that if two states (PV) are equal and their internal energies (U) are different (because the work done to get to each state is different) then it follows that there must be an enthalpy change in doing so.
III. You can use the fundamental thermodynamic relation to solve for the difference in internal energy between both states.
IV. This one's the easiest. Assuming no mass is lost: n is constant, R is constant, you know the Ps and Vs, solve for delta(T) for each case (using the ideal gas law).
*Disclaimer - I'm very rusty with my thermo so all of this might be completely wrong and I defer all liability to Bush/Obama (depending on your political preference).
