Thermodynamics problem How to find the temperature of a gas.

[UCstudent]

Thermodynamics problem! How to find the temperature of a gas. Please Help!

Homework Statement

In an engine, 0.45 moles of gas at 1050 degrees K in a cylinder expand adiabatically against the piston. The gas does 3200 J of work against the piston. What is the final temperature of the gas?

Homework Equations

What formula do I use?

The Attempt at a Solution

The only formula I can think to use is

W=(-P)(delta V)

But pressure and volume aren't given, and I can't find them with the given information.

 

[ehild]

Assume that the gas is ideal and apply the ideal gas law together with the First Law of Thermodynamics.

ehild

 

[UCstudent]

How do you apply the first law of thermodynamics?

 

[Andrew Mason]

How do you apply the first law of thermodynamics?

First law: Q = ΔU + W where W = work done by the gas.

Here you are given Q and W. You first have to determine ΔU.

In order to find the change in temperature, however, you have to know the relationship between ΔU and ΔT. That depends on the gas. Are you given the Cv of the gas?

AM

 

[ehild]

What have you learned about adiabatic expansion of a gas? What is the relation among pressure and volume during such a process?
Anyway, you need to know the ratio Cp/Cv. You do not need the initial volume and pressure to solve the problem.
Collect all equations you know and are relevant: The ideal gas law, the adiabatic equation of state (you can derive it using the First Law if you do not know it) and the expression of work done by the gas.

ehild

 

[Andrew Mason]

I don't think the adiabatic condition applies here since there is no indication that it is a quasi-static adiabatic expansion. Besides, one would need to know either P or V as well as T. However, we do need to know Cv to solve the problem

AM

 

[ehild]

I don't think the adiabatic condition applies here since there is no indication that it is a quasi-static adiabatic expansion. Besides, one would need to know either P or V as well as T. However, we do need to know Cv to solve the problem

AM

You are right, we do not need to assume a quasi static process. But we need to know if it is an ideal gas and the number of atoms in its molecules, or Cv for the internal energy. .

ehild

 

[netgypsy]

Sounds like you have to assume ideal gas

 

[UCstudent]

Thank you for your help!

 

[netgypsy]

No problem - guess you got it :-)

 

[UCstudent]

I sure did! :) Can you help me with my new problem? lol

 

[netgypsy]

point me to it

 

[UCstudent]

https://www.physicsforums.com/showthread.php?t=559630