If you were to cut off a little piece of sodium, and place it into water, you would end up getting some sodium hydroxide produced, that's dissolved in the water, and some hydrogen gas. And you would generate some heat. This is an exothermic reaction, as the negative sign indicates. When we look at this thermochemical equation that's presented here, this amount of heat is generated when we look at these quantities in terms of mole amounts. So when two moles of sodium reacts with two moles of water, you will produce two moles of sodium hydroxide, one mole of hydrogen gas in this amount of heat. This problem is giving us information about the sodium. And so we're putting a little bit of sodium into an excess of water. So if we look at this relationship, we know that 368.4 kilojoules of heat will be generated every time two moles of sodium reacts. And we're going to use that piece of information to then determine how much heat is evolved, given off, or absorbed, was given off because it's exothermic. If 1.5 grams of sodium reacts. Well since our relationship is not with grams but with, with moles, I know I need to take the 1.5 grams of sodium and I need to convert it to moles of sodium. And there are 22.99 grams of sodium in a mole. This will get me to the moles of sodium, which then will allow me to use the relationship that I wrote above. Moles of sodium to kilojoules. We know that we are going to generate 368.4 kilojoules for every two. Don't forget that two. There's a two right here. Two moles of sodium. Now this will give me the answer to the question and that is going to be to two significant figures, 12 kilojoules. Now, very often, in a problem, you're given a thermochemical equation. And this will be a tool that you will use to figure out how much heat is given off for a specific amount. So, you'll look at your balanced equation. You'll look at the quantities that are given, and you'll be able to determine, using that ratio, how much heat is given off.