Name____________________________________________ Period__________ energy ws3 Energy of Heating and Cooling Water
In the previous worksheet we learned to use the specific heat equation:
q = mcT
(where q = joules of heat, m = grams of mass, c = specific heat in j/gOC, and T = degrees of temperature change) To heat or cool water we have to consider the phase it is in, as well as the energy associated with phase changes Symbol and value Symbol What it means o The specific heat of liquid water It takes 4.18 joules of heat cwater(l) = 4.18 J/g C energy to raise the temperature of 1 gram of liquid water by one degree Celsius o The specific heat of ice It takes 2.03 joules of heat cwater(s) = 2.03 J/g C energy to raise the temperature of 1 gram of solid water (ice) by one degree Celsius o The specific heat of steam It takes 2.01 joules of heat cwater(g) = 2.01 J/g C energy to raise the temperature of 1 gram of gaseous water (steam) by one degree Celsius Hvap = 2,259 J/g The enthalpy of vaporization of It takes 2,259 joules of water energy to boil one gram of liquid water (convert it from a liquid to a gas). Hfus =334 J/g The enthalpy of fusion of water It takes 334 joules of energy to melt one gram of liquid water (convert it from a solid to a liquid). To find out how much energy it takes to heat water, we may have to include the energy of phase changes. For example, there are five separate energy steps involved when ice is heated into steam: 1. The ice warms to 0OC 2. The ice melts at 0OC 3. The water heats to 100OC 4. The water boils at 100OC. 5. The steam raises to it’s final temperature. Note for the last step we assume a closed system that would pressurize. Use these ideas to answer the guided questions below. 20