# Reversible Heating and Cooling

## Homework Statement

I have two problems.

What is Delta U, Delta H, q, and w for the Reversible heating of an ideal gas at constant P.

Also, what are these values for the Reversible cooling of an ideal gas at constant V.

## The Attempt at a Solution

For the first equation I decided that all values would be negative except for heat which is positive. I consider this because w=-pex(deltaV) and I decided q= positive because when u are heating somethign you add heat.

for the second problem I know work=0 because the system is at constant volume. Also, q=Delta U because Delta U=q+w. q is negative because soemthing that is cooling is removing heat. I can not figure out delta H.

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Redbelly98
Staff Emeritus
Homework Helper
Welcome back to PF Are you being asked to provide the expressions for ΔU, etc., in terms of P and V? Or just to state whether they are positive, negative, or zero?

For the first equation I decided that all values would be negative except for heat which is positive. I consider this because w=-pex(deltaV) and I decided q= positive because when u are heating somethign you add heat.
That's good reasoning on w and q. How did you figure out that U and H are negative?

for the second problem I know work=0 because the system is at constant volume. Also, q=Delta U because Delta U=q+w. q is negative because soemthing that is cooling is removing heat.
Looks good so far.
I can not figure out delta H.
What is the definition of H?

Also, the fact that it is an ideal gas might or might not come into play.

H is enthalpy. I just have to say whether or not the values of these will increase decrease or if they are zero in each case. I am really only concerned about the last two.

Redbelly98
Staff Emeritus