# Homework Help: What is the mass of the helium present - Thermodynamics

1. Jan 10, 2006

### cmilho10

A sample of helium behaves as an ideal gas as energy is added by heat at constant pressure from 273 K to 383 K. If the gas does 23.0 J of work, what is the mass of helium present?

I tried this and think u use m=Q/c*change in T, but not sure where to go from there

2. Jan 10, 2006

### Michael_McGovern

The expression for the work done by the gas is:
$$dW=PdV$$
Since there is constan pressure we can write:
$$V=\frac{nRT}{P}$$
$$dV=\frac{nR}{P}dT$$
So
$$dW=nRdT$$
and
[/tex]W=\int_{T_1}^{T_2}nRdT[/tex]
Do the integral, use the molar mass of He to convert the # of moles of He to the mass, and then solve for the mass.