- #1

Trenthan

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## Homework Statement

Ok, i have a cycle that goes from "a to b", via isobaric expansion, than from "b to c" vis isochoric decrease in pressure, and "c to a" via a adiabatic compression. Each occur under quasistatic conditions

I just want to double check I've got the, changes in work, heat, internal energy, enthalpy and entropy right

## The Attempt at a Solution

Process "a to b", isobaric expansion

a) Work is negative due to expansion

b) Q (heat) is added to the system hence Q is positive

c) U, internal energy increases due to us adding heat

d) Enthalpy inceases, since Q is positive

e) entropy increases since volume increases due to the number of microstates increasing in the system

Process "b to c", isochoric decrease in pressure

a) W = 0, no change in volume

b) Q(heat) is negative since heat is taken from the system to decrease pressure

c) U internal energy is negative since temperature decreases as heat is removed

d) Enthalpy is negative as heat is removed

e) entropy is negative since the nubmer of possible microstates decreases since there is less energy in the system ***Can it be negative my understanding is it can only be positive or zero***?

Process "c to a", adiabatic compression

a)W is positive since we compress the gas

b) Q = 0 since it happen so quick no heat flow into or out of the system

c) U internal energy is positive since temp increases

d) enthalpy is zero, i no this from the formula but why,, internal energy increases, and positive work is done on the gas, hence shouldn't it be positive?

e) Entropy I've read its zero, i cannot work out how mathematically it was determined, and am a little stuck with understanding as to why? i would have thought negative since we decrease the volume hence fewer microstates in the system

Im mainly concerned with the red parts, they seem pritty iffy, and my textbook is just mass confusion is those areas with teh explanation lolz

Thanks heeps