Document

advertisement
Section 12.4 Assessment
The addition of energy to water molecules
will cause them to ____.
A. freeze
B. change to water vapor
D
A
0%
C
D. move closer together
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. form a crystal lattice
Section 12.4 Assessment
The transfer of energy from one object to
another at a lower temperature is ____.
A. heat
B. degrees
D
A
0%
C
D. electricity
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. conductivity
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.
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.
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.
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.
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
Measuring Heat (cont.)
• Example:
• A candy bar has 245 Calories. Convert this to calories
and then to Joules of energy.
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.
Specific Heat (cont.)
• Calculating heat absorbed and released
– q = c × m × ΔT
– q = heat absorbed or released (in Joules)
– c = specific heat of substance
– m = mass of substance in grams
– ΔT = change in temperature in Celsius
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 × ΔT
• Specific Heat of Ice = 2.03 J/goC
• 1 calorie = 4.184 J
Specific Heat (cont.)
• Example Cont.




q=?
c = 2.03 J/goC
m = 23.0 grams
ΔT = FinalTemp(0.0oC) – InitialTemp (-27.0oC) = Change (27.0oC)
 q = c × m × ΔT
q = (2.03 J/goC)(20.0g)(27.0oC)=
• 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 × ΔT
To make the problem
easier, solve for the
unknown BEFORE you
plug in the numbers.
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)
• 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?
Section 15.1 Assessment
The heat required to raise one gram of
a substance by one degree Celsius is
called ____.
A. joule
A
0%
D
D. energy
C
C. specific heat
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. calorie
Section 15.1 Assessment
Which of the following is an example of
chemical potential energy?
A. the moon orbiting Earth
B. a car battery
D
A
0%
C
D. a roller coaster at the top of a hill
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. a compressed spring
• Aluminum has a specific heat of 0.897 J/(g ºC). What
does this mean?
Download
Related flashcards

Fire

14 cards

Refractory materials

29 cards

Heat transfer

25 cards

Create Flashcards