OK, so I'm suppose to calculate how many grams of propane are required to heat all of the water in a 50 gallon water heater from 23.4 C to 65.0 C if the water heater (the jacket which contains the water) itself has a heat capacity of 23.4 J/C and the heater also uses 2.3 kg of copper pipe.

SO, would I use -q

_{sys} = q

_{surr}And set the heat of water equal to the heat of the water heater?

My problem is the question of where the water heater's capacity comes into place, and whether or not I also need the specific heat capacity of copper.

Furthermore, I can't think of a way to properly use Hess's Law (except to calculate the heat released by burning 1 mole of propane).

Any direction/help? I've done numerous problems, but nothing like this so far, and it's getting quite complex, I think...

Also, is 50 gallons are equivalent to 189,270 grams, right?