First Law of Thermodynamics and ideal gas

[brutalmadness]

Homework Statement

An ideal gas expands isothermally, performing 3.40x10^3 J of work in the process.
a) The change in internal energy of the gas
b) The heat absorbed during this expansion

Homework Equations

\DeltaU=Q-W

The Attempt at a Solution

a) Since it's isothermally expanding, there will be no change in internal temperature, so:
\DeltaU=0

b) Q=W, so:
Q=-3400 J

 

[Mapes]

Looks good, as long as positive heat means that the system is heating the environment and positive work means that the environment is doing work on the system. This sign convention is a little unconventional, though.

 

[Doc Al]

b) Q=W, so:

Good.

Q=-3400 J

How did that negative sign sneak in? (W is positive, so Q is positive.)

 

[brutalmadness]

Ah, ok. That was a silly mistake, lol :)

So Q=3400 J