## delta U for Isothermal Expansion of Ideal Gas

$\Delta U=q+w$

Lily Guo 1D
Posts: 64
Joined: Fri Sep 29, 2017 7:03 am

### delta U for Isothermal Expansion of Ideal Gas

Why does delta U = 0 for the isothermal expansion of an ideal gas?

Tiffany 1B
Posts: 32
Joined: Fri Sep 29, 2017 7:05 am

### Re: delta U for Isothermal Expansion of Ideal Gas

The equation for an ideal gas is U=3/2*nRT. When you're calculating the change in internal energy, the number of moles and the gas constant are constant values and that means the change in internal energy is dependent upon temperature change. But in an isothermal expansion temperature doesn't change. Therefore, delta T=0 and U=3/2*nR*(0)=0. Hope that helps.

Lily Guo 1D
Posts: 64
Joined: Fri Sep 29, 2017 7:03 am

### Re: delta U for Isothermal Expansion of Ideal Gas

Tiffany 1B wrote:The equation for an ideal gas is U=3/2*nRT. When you're calculating the change in internal energy, the number of moles and the gas constant are constant values and that means the change in internal energy is dependent upon temperature change. But in an isothermal expansion temperature doesn't change. Therefore, delta T=0 and U=3/2*nR*(0)=0. Hope that helps.

Thank you, that was super helpful!