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 occurringWhen 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).

  1. 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

  1. 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)

  1. 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.

  1. 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.

  1. What is the formula used to determine the amount of heat gained or lost?

Heat = mass x change in temp x specific heat

  1. What units is heat measured in?

Calories

  1. 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)

  1. 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

  1. 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

  1. Name 3 examples of good insulators. Air, glass, wood, Styrofoam, plastic
  1. 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