Energy: Worksheet 4 Name
Quantitative Energy Problems (Part 2) 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
For each of the situations:
· Sketch a Temperature vs. Time graph (warming / cooling curve) to show what is happening to the temperature of the substance. Label any critical temperatures that you know on the graph.
· Describe, in your own words, what is happening. Make sure to include the states of matter that are involved as well as any phase changes that are taking place.
· Identify what relationships (equations) are applicable to each section.
· Identify what constants you will use based on the phase or phase change process.
· Rearrange the equation if necessary and plug in the numbers with units. Keep a reasonable number of sig figs in your answers.
1. How much energy is absorbed by 150 g of ice at 0.0 ˚C that melts and then warms to 25.0˚C?
a. Sketch the temp vs. time graph and split your graph into different sections. Label each section with the phase(s) that are present.
b. Describe what is happening
c. For each section, pick the equation that you will use and the
constant that you will use.
d. Solve for the energy for each section as well as the total energy that is absorbed by the water.
2. Suppose in the Icy Hot lab that the burner transfers 325 kJ of energy to 450 g of liquid water at 20.˚C. What mass of the water would be boiled away?
a. Sketch the temp vs. time graph and split your graph into different sections. Label each section with the phase(s) that are present.
b. Describe what is happening
c. For each section, pick the equation that you will use and the constant that you will use.
d. Solve for the energy in the first section.
e. How should the energy for each section compare to the total energy that is absorbed by the water?
f. Solve for the mass of water that is boiled away.
3. A 12oz can of soft drink (assume m = 340 g) at 25˚C is placed in a freezer where the temperature is – 12 ˚C. How much energy must be removed from the soft drink for it to reach this temperature?
a. Sketch the temp vs. time graph and split your graph into different sections. Label each section with the phase(s) that are present.
b. Describe what is happening
c. For each section, pick the equation that you will use and the constant that you will use.
d. Solve for the energy in each section.
4. 65.0 kilojoules of energy are added to 150 g of ice at 0.0˚C. What is the final temperature of the water?
a. Sketch the temp vs. time graph and split your graph into different sections. Label each section with the phase(s) that are present.
b. Describe what is happening
c. For each section, pick the equation that you will use and the constant that you will use.
d. Solve for the energy in the first section.
e. With the remaining energy, solve for the change in temperature.
Answer Key: 1) 66kJ 2) 77g 3) 160kJ 4) 24°C
Modeling Chemistry 1 EnergyWS4-nh2.doc