There is 30g of ethanol dissolved in 63g of water. the molar mass of ethanol is 46.07g/mol. how many moles of water are there?

Since you are only looking for how many moles are in water, the 30 g grams of ethanol are irrelevant in this case. You know that there are 63 g of water. In order to calculate the amount of moles, you must know the molar mass of water. In order to calculate the molar mass you have to add the average atomic mass of two hydrogen and one oxygen (H2O). This is 18.02 g/mol. Now you would divide the given number of grams (63 g) by the molar mass (18.02 g/mol) and you would then get your answer, which is about 3.5  (3.496)

They can measure  the amount of energy gained or lost