## Delta U

$\Delta U=q+w$

Michael Du 1E
Posts: 117
Joined: Sun Sep 22, 2019 12:16 am

### Delta U

Under what conditions would Delta U = 0 and q = -w ? Thank you

805383532
Posts: 53
Joined: Thu Jul 11, 2019 12:16 am

### Re: Delta U

delta U is equal to 0 when temperature is constant. If delta U is 0, and deltaU=q+w, then 0=q+w and when you solve for q then the equation becomes q= -w

Jared_Yuge
Posts: 100
Joined: Sat Aug 17, 2019 12:17 am

### Re: Delta U

delta U can be 0 when a system is doing work as a reversible expansion and when the energy lost is replaced by heat flow into the system (isothermic).

Helen Struble 2F
Posts: 97
Joined: Sat Aug 24, 2019 12:17 am

### Re: Delta U

Isothermal systems have delta U = O because the transfer of heat and pressure are both at equilibrium, so all the energy lost by the work of expansion transfers into the system as heat in order to keep the temperature constant. Since work is being done (system losing energy), -w is negative, and since heat is transferring in (gaining energy), q is positive. If these values were not equal, delta U would not equal zero and the system would not be truly isothermal.

J_CHEN 4I
Posts: 54
Joined: Tue Nov 14, 2017 3:01 am

### Re: Delta U

delta U = 0 for isothermal expansion or compression of an ideal gas. delta U = 0, when q = 0 and w = 0 (since delta U = 0 + 0 = 0). q = -w when delta U = 0, then 0 = q + w, which is q = -w.

Owen-Koetters-4I
Posts: 50
Joined: Fri Sep 28, 2018 12:16 am

### Re: Delta U

isothermal compression or expansion

Ashley Nguyen 2L
Posts: 103
Joined: Sat Aug 17, 2019 12:18 am
Been upvoted: 1 time

### Re: Delta U

DeltaU = 0 when there is an isothermal expansion. Although work is used, and heat is consequently lost, heat flow from the surroundings replaces the heat lost, so temperature remains constant. If we know that deltaU = 0, and that deltaU = w + q, then q = -w. We can confirm that w is a negative value because work is being done by the system (system is losing heat/energy).

Yiyang Jen Wang 4G
Posts: 76
Joined: Wed Nov 21, 2018 12:18 am

### Re: Delta U

Delta U=0 for Isothermal compression or expansion (at constant temperature).