# Homework Help: Ideal gas law

1. Apr 21, 2005

### ~angel~

A Jaguar XK8 convertible has an eight-cylinder engine. At the beginning of its compression stroke, one of the cylinders contains 499cm^3 of air at atmospheric pressure (1.01×105 Pa and a temperature of 27.0 C. At the end of the stroke, the air has been compressed to a volume of 46.2 cm^3 and the gauge pressure has increased to 2.72×106 Pa. Compute the final temperature.

I ended up with 69.8 degrees. I used the ideal gas law, but because the mass of air remains constant, i used:

(p1v1/T1) = (p2v2/T2)

I converted the volume to 4.99 x 10^-4 and 4.62 x 10^-5. I also dtermined the final absolute pressure, which is 2.821 x 10^6. But my answer is wrong. Could someone please help.

2. Apr 21, 2005

### ~angel~

It's ok...i forgot to convert to Kelvin.

3. Apr 21, 2005

### dextercioby

Classical mistake.The weird part is that u converted the volume...

Daniel.

4. Apr 21, 2005

### ramollari

Use the ratios of the volumes, so as dex said you don't need to convert. Also, as you understood, always work with Kelvin!

5. Apr 21, 2005

### dextercioby

I hope u see that u need the conversion to K in both the initial & final temperature...

Daniel.

6. Apr 21, 2005

### ussrasu

How did you find the final absolute pressure?