# Thermal Properties: Pressure, Volume, Temp question

wcbryant87

## Homework Statement

A Jaguar XK8 convertible has an eight-cylinder engine. At the beginning of its compression stroke, one of the cylinders contains 499 cm cubed of air at atmospheric pressure (1.01E5 Pa) and a temperature of 27.0 degrees C. At the end of the stroke, the air has been compressed to a volume of 46.2 cm cubed and the gauge pressure has increased to 2.72E6.

What is the final temperature

## Homework Equations

P1*V1/T1 = P2*V2/T2

## The Attempt at a Solution

I followed the equation that I posted above. Here is what it looked like.

(1.01E5 * 499 cm cubed)/ 27 = (2.72E6 * 46.2)/x

Solving for x, I got x = (2.72E6*46.2)/1866629.63 = 66.8 degrees C

Problem is, that answer is apparently wrong. Am I missing something here?

Thanks for the help!

Lambduh
Try changing your temperature to kelvin :)

wcbryant87
well it wants the answer in celcius. Does that equation have to be done with Kelvin units?

xxChrisxx
Were you given that equation? As you wont find T2 like that. Even if you use kelvin as the pv/pv is a ratio, it wont make any difference.

Hint: Expansion and compression is isentropic.

wcbryant87
No I wasn't given any equation. I thought that that one would work though because I was only missing one variable.

Do I use pv=nrt?

xxChrisxx
If you've got a book, look up isentropic compression.

pv^gamma = constant.

where gamma is the polytropic constant you'll have to find the relationship between temperature and anther variable.

Gorz
If you've got a book, look up isentropic compression.

pv^gamma = constant.

where gamma is the polytropic constant you'll have to find the relationship between temperature and anther variable.