Energy - Worksheet 3 Name
Quantitative Energy Problems Date Pd
Energy constants (H2O)
334 J/g Heat of fusion (melting or freezing) ΔHf
2260 J/g Heat of vaporization (evaporating or condensing) ΔHv
2.1 J/g˚C Heat capacity (c) of solid water
4.18 J/g˚C Heat capacity (c) of liquid water
1. In the cooling curve at right, identify the section where the temperature is changing and the section where the phase is changing.
For each of the following problems:
a. Sketch a warming or cooling curve to help you decide which equation(s) to use to solve the problem.
b. Keep a reasonable number of significant figures in your answers.
c. Show all your work (including any conversions)
2. A cup of coffee (140. g) cools from 75˚C down to comfortable room temperature 20.˚C.
a. How much energy does it release to the surroundings?
b. Convert your answer to kilojoules (kJ) – Setup and show all work
3. Suppose during PE, you lose 2.0 lbs of water due to sweating.
a. Convert 2.2 lbs à grams 2.2 lbs = 1.0 kg
b. If all of this water evaporates, how much energy does the water absorb from your body? Express your answer in kJ.
4. A bag full of ice (450. g) at 0.0 ˚C sits on the counter and begins to melt to liquid water. How much energy is absorbed by the ice when 2/3 of it melts?
5. Suppose that during the Melting Ice lab that 65 kJ of energy transferred to 450. g of water at 20˚C. What is the final temperature of the water?
6. The heat capacity of solid iron is 0.447 J/g˚C. If the same quantity of energy as in #5 (65 kJ) is transferred to a 450. g chunk of iron at 20.˚C, what is the final temperature?
7. Water has a relatively high heat capacity compared to other substances. What advantage is there for people living near large bodies of water (like Lake Michigan or the ocean)?
8. A serving of Cheez-Its releases 130. kcal (1 kcal = 4.18 kJ) when digest it.
a. Convert 130 kcal à Joules
b. If this same amount of energy transferred to water at its boiling pt, what mass of water is vaporized?
Answers: 2a) 32186 J 3b) 2055 kJ 4) 99 kJ 5) 54°C 6) 343°C 8b) 240g
Modeling Chemistry 2 Energyws 3-nh2.doc