 OK, so let's do a problem on calculating the molar volume. So this problem says a helium weather balloon was filled at negative 20 degrees Celsius to a volume of 2.5 times 10 to the fourth liter with 1.2 times 10 to the third moles of helium. What is the molar volume of helium at negative 20 degrees Celsius? So recall the molar mass, I think is a good way to think about this, is the molar mass is a conversion between the number of grams a mole takes up. So this would be something very similar to that. This would be like the number of liters a mole takes up of a gas in this case. But the molar volume is in units of moles per liter. So that should give you a clue as to how to set this up. So the molar volume is going to be a volume 2.5 times 10 to the fourth liter divided by 1.2 times 10 to the third mole. So this would be the molar volume of helium at negative 20 degrees Celsius. OK, so to two-stick fix, I get this to be 21 liters per mole of helium. So at negative 20 degrees Celsius, the molar volume of helium would be 21 liters. Is everybody OK with thinking like that? OK, again, I'd like to equate this somewhat to that molar mass we were talking about. OK?