What is the change in the heliums internal energy in units...

What is the change in the helium's internal energy in units of kilojoules, kJ? Calculate the work done on or by the helium gas in units of joules, J. A total of 24.1 kJ of heat energy is added to a 6.21 L sample of helium at 0.981 atm. The gas is allowed to expand against a fixed external pressure to a volume of 20.4 L .

Transcript

00:01 So for this question, you're asked to find the work done by the helium gas and also the change in internal pressure.

00:08 So first we're going to calculate the work because we're going to need that number in order to calculate the internal energy.

00:16 So in order to calculate the work, we are going to use the equation where work equals a negative pressure times the change in volume.

00:27 We are told that the pressure is held constant at 0 .91 atmospheres and that the gas expands from 6 .21 liters to 20 .4 liters.

00:39 So i have them labeled as the initial volume vi and the final volume bf.

00:46 So first we'll calculate work.

00:48 So work is going to equal negative times our pressure of 0 .981 atmospheres.

00:59 Times our change in volume, which is the final volume minus the initial volume.

01:05 So we'll say 20 .4 liters minus 6 .21 liters.

01:13 And then just type that into your calculator and you should get a negative number, right, because it's negative here.

01:24 And you should get negative 13 .92 liters per atoms.

01:30 However, we're asked to find the work done in joules.

01:33 So we have to convert liters at atoms to jewels.

01:36 So we'll just do a simple unit conversion.

01:39 So we have negative 13 .92 liters per atoms.

01:45 So we'll take that times 101 .3 joules because there's 101 .3 joules for every one liter times atom.

01:54 So we'll see our unit conversion.

01:56 The units will cancel.

01:58 So we'll be left for the joules.

01:59 So type that in your calculator, negative 13 .92 times 101 .3...

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