A

1
Section 12-4
Section 12.4 Assessment
The addition of energy to water molecules will
cause them to ____. A. freeze B. change to
water vapor C. form a crystal lattice D. move
closer together

1. A
2. B
3. C
4. D

2
Section 12-4
Section 12.4 Assessment
The transfer of energy from one object to another
at a lower temperature is ____. A. heat
B. degrees C. conductivity D. electricity

1. A
2. B
3. C
4. D

3
Section 15-1
Section 15.1 Energy (cont.)
energy law of conservation of energy chemical
potential energy heat calorie joule specific heat
Energy can change form and flow, but it is always
conserved.
4
Section 15-1
The Nature of Energy

• Energy is the ability to do work or produce heat.

• Two forms of energy exist, potential and kinetic.
• Potential energy is due to composition or
  position.
• Kinetic energy is energy of motion.

5
Section 15-1
The Nature of Energy (cont.)

• The law of conservation of energy states that in
  any chemical reaction or physical process, energy
  can be converted from one form to another, but it
  is neither created nor destroyed.
• This is also known as the first law of
  thermodynamics.

6
Section 15-1
The Nature of Energy (cont.)

• Chemical potential energy is energy stored in a
  substance because of its composition.

• Chemical potential energy is important in
  chemical reactions.
• Heat is energy that is in the process of flowing
  (transferring) from a warmer object to a cooler
  object.
• q is used to symbolize heat.

7
Section 15-1
Measuring Heat

• A calorie is defined as the amount of energy
  required to raise the temperature of one gram of
  water one degree Celsius.

• Food is measured in Calories, or 1000 calories
  (kilocalorie).
• A joule is the SI unit of heat and energy,
  equivalent to 0.2390 calories.
• 1 calorie 4.184 J or 1 J 0.2390 calories

8
Section 15-1
Measuring Heat (cont.)
9

• Example
• A candy bar has 245 Calories. Convert this to
  calories and then to Joules of energy.

10
Section 15-1
Specific Heat

• The specific heat of any substance is the amount
  of heat required to raise one gram of that
  substance one degree Celsius.

• Some objects require more heat than others to
  raise their temperature.

11
Section 15-1
Specific Heat (cont.)

• Calculating heat absorbed and released

• q c m ?T
• q heat absorbed or released (in Joules)
• c specific heat of substance
• m mass of substance in grams
• ?T change in temperature in Celsius

12
Specific Heat (cont.)

• Examples
• How much heat does a 20.0 g ice cube absorb as
  its temperature increases from (-27.0oC) to
  0.0oC? Give your answer in both joules and
  calories.
• q c m ?T
• Specific Heat of Ice 2.03 J/goC
• 1 calorie 4.184 J

13
Specific Heat (cont.)

• Example Cont.
• q ?
• c 2.03 J/goC
• m 23.0 grams
• ?T FinalTemp(0.0oC) InitialTemp (-27.0oC)
  Change (27.0oC)
• q c m ?T
• q (2.03 J/goC)(20.0g)(27.0oC)

14

• Example 2
• A 5.00 gram sample of a metal is initially at
  55.0 ºC. When the metal is allowed to cool for a
  certain time, 98.8 Joules of energy are lost and
  the temperature decreases to 11.0º C. What is the
  specific heat of the metal? What metal is it?
• q c m ?T

To make the problem easier, solve for the unknown
BEFORE you plug in the numbers.
15
Measuring Heat

• For Water during a phase change
• The Heat of Fusion (melting) is 334 j/g
• The Heat of Solidification (freezing) is 334 j/g
• They are the same value (energy in or out)
• The Heat of Vaporization is 2260 j/g
• The Heat of Condensation is 2260 j/g
• They are the same value (energy in or out)

16

• Example Phase change
• Calculate the amount of energy needed to convert
  55.0 grams of ice to all liquid water at its
  normal melting point.
• Using the same amount of water calculate the
  energy needed to completely vaporize the water at
  its normal boiling point.
• Why is there such a large difference in energy
  needed?

17
Section 15-1
Section 15.1 Assessment
The heat required to raise one gram of a
substance by one degree Celsius is called ____.
A. joule B. calorie C. specific heat
D. energy

1. A
2. B
3. C
4. D

18
Section 15-1
Section 15.1 Assessment
Which of the following is an example of chemical
potential energy? A. the moon orbiting Earth
B. a car battery C. a compressed spring D. a
roller coaster at the top of a hill

1. A
2. B
3. C
4. D

19

• Aluminum has a specific heat of 0.897 J/(g ºC).
  What does this mean?