## delta U for an ideal gas expansion

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

Elizabeth Bowen 1J
Posts: 53
Joined: Wed Nov 14, 2018 12:20 am

### delta U for an ideal gas expansion

can anyone explain why delta U=0 for an isothermal ideal gas expansion/compression?
thanks

AArmellini_1I
Posts: 107
Joined: Fri Aug 09, 2019 12:15 am

### Re: delta U for an ideal gas expansion

Because isothermal means energy/heat and matter cannot leave or enter the system, therefore the internal energy of the system (delta U) is constant

Elizabeth Bowen 1J
Posts: 53
Joined: Wed Nov 14, 2018 12:20 am

### Re: delta U for an ideal gas expansion

Thanks, if we were told that a gas expansion is isothermal, do you think that we should assume it's an ideal gas if not specified (so that we can use the fact that delta U=0)?

AArmellini_1I
Posts: 107
Joined: Fri Aug 09, 2019 12:15 am

### Re: delta U for an ideal gas expansion

Elizabeth Bowen 1J wrote:Thanks, if we were told that a gas expansion is isothermal, do you think that we should assume it's an ideal gas if not specified (so that we can use the fact that delta U=0)?

Yeah I believe so! But I don't think whether or not it is an ideal gas influences delta U = 0. I'm pretty sure that statement is true for all isothermal systems.