To find our number of moles. If we find that we have three knowns and one unknown, we'll suffer that unknown, namely this guy, and we'll get our answer. So to find the number of moles n, we simply take our number 0.5
grams of methane. Divide that by our molecular weight of methane grams cancel and we get moles on top. So 0.5
grams divided by 16 is 132, which is 0.3125 moles. We take this moles, plug it into our formula along with not 25 degrees Celsius, but 273 plus 25.