An ideal gas expands isothermally, performing 4.4*10^3 J of work in the process. Calculate a) the change in internal energy of the gas and b) the heat absorbed during this exapnsion.

Question

jennychan12 · Answer

for part a) i know i'm trying to find ΔU but doesn't that mean i have to find Q? but to find Q i need a mass and it's not given.

jennychan12 · Answer

so this is the work

jennychan12 · Answer

^ the numbers are different, but it's the same idea.

kainui · Answer

So basically since it's isothermal we can see from this equation derived from heat capacity that internal energy change is 0:

$$\Delta U=Cv \Delta T$$
So we can take this result and allows us to see from the first law of thermodynamics that the heat and work are opposites, so the amount of energy entering as heat is equal to the amount of energy leaving as work to push out at the piston or whatever it's contained in.

U=q+w

q=-w

kainui · Answer

I can explain anything in more detail if you're having trouble with it, it took me forever to finally get these ideas to click in my brain. lol

jennychan12 · Answer

Sorry, can you just assume that the temperature is constant?

kainui · Answer

You're not assuming it, they're telling you that temperature is constant.

The definition of an "isothermic" process is one that occurs at constant temperature. "Iso" means same "thermo" means temperature.

So if the temperature is the same throughout, that means the change in temperature is 0.

In my mind every time I see isothermal I think:

T=constant
Delta T=0

jennychan12 · Answer

ohhh sorry. my teacher didn't really explain what isothermic meant.

kainui · Answer

No problem. =D Also, similarly an adiabatic process is one where there is no heat transfer, so q=0 every time you are dealing with adiabatic processes. This also means that U=w for adiabatic processes, which is very useful!

jennychan12 · Answer

ohhh that makes so much more sense. sorry my teacher just like rushed through the lesson, without really explaining what those term meant.

kainui · Answer

Yeah, if you have anymore questions I'd totally be happy to help. I just finished taking Physical Chemistry I last semester so it's still pretty fresh in my mind.