Dehydrated meals carried on camping trips are reconstituted with hot water. The energy used to heat the

Question:

Dehydrated meals carried on camping trips are reconstituted with hot water. The energy used to heat the water is typically supplied by burning fuel in a camp stove. How much energy is required to heat the water? Calculate the heat necessary to increase the temperature of

(a) 100. g of water,

(b) 2.00 mol H₂O(l) from 20.°C to 100.°C.

ANTICIPATE Because the molar mass of water is about 18 g · mol^–1, 100 g of water is greater than 2.00 mol H₂O, so you should expect more heat to be required for (a) than for (b).

PLAN The heat required is given by Eq. 6. For (a), use the specific heat capacity and for (b), use the molar heat capacity. In each case, ΔT = 180. K. Note that a heat capacity expressed in J · (°C)^–1 · g^–1 is numerically the same when expressed in J · K^–1 · g^–1.

What should you assume? Assume that no energy is lost to the container or the surroundings during the heating and that the water is thoroughly mixed, so that it is at the same temperature throughout.