We quantified the work done by a gas by looking at the pressure-volume graph, which was easy. We quantified the internal kinetic energy of the gas, which was much harder. The metaphor we used was that of the Koopa Troopa, the Mario turtle that, if you step on it, can bounce back and forth from wall to wall at the same speed forever. It's a good model of many, many elastic collisions even if it isn't realistic. It does require some handwaving to get the derivation, but we know have an expression for the kinetic energy of one molecule of a gas. It also allowed us to explain why there's not much hydrogen gas in our atmosphere.
We then previewed the heat engine lab. We have a lot of practice to do before we get to that lab.