Heat Energy Review Sheet
Definitions- define the following in your own words (I didn’t fill these out since you can
look ‘em up yourself )
Heat:
Conductor:
Insulator:
Temperature:
Specific Heat:
Phase Change:
Heat of Fusion:
Heat of Vaporization:
Calorie:
Absolute Zero:
Kinetic Energy:
Short Answer: answer each of the following questions in detail
1. Give an example from your daily life of heat transfer by each of the three methods.
Then describe exactly how the transfer occurs in your example.
First method example: Conduction occurs when you eat a popsicle.
Describe how the heat transfer is occurring
The molecules in your tongue are vibrating faster since they have more heat. As
they come in contact with the cooler molecules in the popsicle, they bump into the
cooler, slower-moving molecules. As they bump the faster moving molecules in your
tongue slow down and the slower moving molecules in your popsicle speed up. This
causes the popsicle to melt
Second method example: Convection occurs when steam rises from my spaghetti pot
Describe how the heat transfer is occurring The hot steam is less dense than the
surrounding air. This is because as gases are heated, they vibrate more. This causes
them to spread out. As they spread out they become less dense and so they rise. As
the steam rises it carries heat upwards
Third method example: radiation
Describe how the heat transfer is occurring When I make my English muffin in
the toaster, the heating element in the toaster gives off invisible rays of infrared light.
This light is absorbed by my English muffin and it causes the molecules to vibrate
faster (heat up).
2. A calorimeter is used to _ measure the heat given by a chemical reaction__. A
reaction is completed inside a calorimeter. There are 500 g of water in the
calorimeter; the temperature of the water increases by 2 degrees celsius. How much
heat did the reaction produce?
Heat = mass x change in temp x specific heat
500 g x 2°C x 1.0 cal/g°C
1,000 cal
3. How much heat is needed to change 10 g of ice into water?
80 cal/g x 10 g = 800 cal (80 cal/g is the heat of fusion for water)
4. How much heat is needed to change 5 g of water into steam?
540 cal/g x 5g = 2700 cal (540 cal/g is the heat of vaporization for water)
5. Above is a graph of the temperature of ice being heated at a constant rate. Explain
why the line does not go up in a straight line. In other words, why is there a spot where
the line flattens out (see arrow)?
Temperature does not increase during a phase change. All the heat goes into breaking the
bonds or forces of attraction between the molecules/atoms. The molecules cannot vibrate
any faster until the bonds are broken and they change phase.
6. Why do substances expand when they are heated?
Molecules begin to vibrate as they are heated. This causes them to bump into each other
and so they spread out.
7. What is the formula used to determine the amount of heat gained or lost?
Heat = mass x change in temp x specific heat
8. What units is heat measured in?
Calories
9. How much heat is needed to raise the temperature of 10 g of wood, 10 degrees
Celsius? Show your work.
Heat = Mass x change in temp x specific heat
= 10g x 10°C x 0.42 cal/g°C (look up specific heat in book on page 24- do
= 42 cal
not need to memorize these)
10. Suppose that 10 g of a substance gained 19.2 cal of heat when the temperature
increased from 70 to 80 degrees Celsius. What would be the specific heat of the
substance? Heat = Mass x change in temp x specific heat
19.2 cal= 10 g x 10 °C x SH
SH = 19.2 cal/10g x 10°C
SH= 0.192 cal/g°C
11. Name 3 examples of good conductors. Gold, copper, silver, aluminum, iron (any
metal)
Good conductors conduct heat easily because They have free electrons that can move
around
12. Name 3 examples of good insulators. Air, glass, wood, Styrofoam, plastic
13. Gases such as air tend to be good insulators because Their molecules are so far
apart that they don’t bump into each other as often