# Help with Ideal Gas problem

1. Nov 19, 2004

### [rit]panfist

Hey, my textbook is not helping at all. Here's the problem followed by what I've done on it so far.

A sample of an ideal gas is taken through the cyclic process abca shown in Fig. 20-20; at point a, T = 241 K.

graph:
http://www.webassign.net/hrw/20_20.gif

There are two parts of the question I could not answer. One is how many moles are in the sample? I plugged the values given into pV = nRT, and I got n = .001248. That answer is incorrect.

Secondly, what is the net heat added to the gas during this cycle? I don't know where to begin for this. The textbook is usually very clear, but for some reason doesn't include anything on this.

If anyone could help me get on the right track, I would greatly appreciate it.

2. Nov 19, 2004

### maverick280857

Do you know the First Law of Thermodynamics?

(Heat Added to a system) = (Change in Internal Energy of system) + (Work done by system on surroundings)

$$dQ = dU + dW$$

Also do you know that at constant volume, dW = 0?

Do you think pV = nRT is valid when V is changing?

Cheers
vivek

3. Nov 19, 2004

### CartoonKid

You should mind your unit. Beware of the pressure which is in $$KN/m_2$$ and not $$N/m_2$$

4. Nov 19, 2004

### CartoonKid

Net heat would be the area bounded by all the 3 lines which is in short the area of the triangle.