Name: _____________________________ Block: _______ Date: __________________
IP 614
Answer Key for Review: Heat, Temperature, Heat Transfer
1. In a copper wire, a temperature increase is the result of which of the following?
A. an increase in the size of the copper particles
B. a decrease in the mass of the copper particles
C. an increase in the motion of the copper particles
D. a decrease in the distance between the copper particles
2. The illustration below shows a student bending a piece of wire back and forth at a single point
X. The wire’s temperature rises noticeably at point X.
Which of the following best describes the source of the temperature increase?
A. Some of the wire’s mass is transformed into heat energy as the wire is bent.
B. Some of the kinetic energy is transformed into heat as the wire is bent.
C. The bending transfers potential energy to the wire, heating it.
D. The bending causes a current that heats the wire.
3. Perfume sprayed from a bottle spreads more easily in a warm room of 25°C than in a cool
room of 15°C. Which of the following correctly compares perfume molecules at 25°C to those at
15°C?
A. At 25°C, they have more mass.
B. At 25°C, they are moving faster.
C. At 25°C, they have less kinetic energy.
D. At 25°C, they are decreasing in volume.
4. The diagram below represents four empty copper containers at room temperature.
An equal amount of water at 90°C is added to each copper container. Assume there is no loss of
heat to the environment. Which container will have had the greatest change in temperature when
the water and the container reach equilibrium?
A. 1
B. 2
C. 3
D. 4
5. Which of the following changes occurs as a solid is heated?
A. The kinetic energy of the solid decreases.
B. The average density of the solid increases.
C. The specific heat capacity of the solid decreases.
D. The average molecular speed in the solid increases.
6.
The graph below represents changes in
molecular motion in a solid plastic
cylinder over time
These changes in the molecules of the
plastic cylinder must be accompanied by
which of the following?
A. an increase in mass
B. a decrease in volume
C. an increase in temperature
D. a decrease in heat capacity
7. Two boxes, A and B, both contain the same number of nitrogen gas molecules.
The gas molecules in box A have twice the average speed of the molecules in box B. Which of
the following best describes the nitrogen gas in box A?
A. The nitrogen gas in box A has a greater mass than the nitrogen gas in box B.
B. The nitrogen gas in box A has a greater density than the nitrogen gas in box B.
C. The nitrogen gas in box A has a greater temperature than the nitrogen gas in box
B.
D. The nitrogen gas in box A has a greater specific gravity than the nitrogen gas in box B.
8. A party shop delivers helium-filled balloons to homes and businesses. The owners realize
from experience that on hot summer days they should inflate the balloons only three-quarters
full. On cold winter days they can fully inflate the balloons. Which of the following is the best
hypothesis to explain this observation?
A. The helium gas is more active in the winter season.
B. Air outside the balloons leaks into the balloons.
C. As the temperature increases, the helium in the balloons expands.
D. Outdoor air pressure in the summer is less than indoor air pressure
9. The illustration below represents an
experiment in which a hot object is added to
a container of water at room temperature.
The water is continuously stirred while the
hot object is immersed in it. Which of the
following graphs best shows the temperature
changes that follow?
Answer: B
10. Which of the following figures correctly
shows the conduction of heat within the
system of metal blocks?
Answer: A
Open Response:
1. The illustration below shows a container of water on an electric hot plate. Point A is in the
water close to the hot plate, and point B is in the water near the top of the container.
The water in the container is at room temperature before the hot plate is turned on.
a. Describe the differences in the average motion of the water molecules at point A and at
point B shortly after the hot plate is turned on.
The average kinetic energy of the molecule at point A is more than the average kinetic
energy of the molecules at point B, (i.e. molecules at A is moving faster than B) because A is
closer to the heat source, therefore initially will have higher temperature than point B
when the hot plate was just turned on.
b. The water is heated until a thermometer placed in the center of the container reaches
100°C. Compare the average motion of the water molecules at points A and B at this
temperature and explain your answer.
After the center of the container reaches 100C, molecules at point A and B will be moving
at the same speed (same average kinetic energy) because convection will allow heat transfer
within the water container so on average molecules will be moving at about the same speed.
c. The hot plate is then turned off. Describe the average motion of the molecules at points A
and B after several hours.
After the hot plate is turned off, since the container is open, lots of the heat will transfer to
the surrounding and eventually reach thermo-equilibrium with the room temperature.
Molecules are point A and B will slow down and transfer heat to the surrounding. The will
be at the same temperature at the end so on average the molecules will be moving slower
than before, but similar between A and B.
Short Answers:
1. What does it mean to say that something is hot? What does it mean to say that
something is cold? Is being hot the presence or absence of something? Why do you
think that?
Being hot means the molecules inside materials are moving faster than the molecules
inside the cold material.
2. What is temperature?
Temperature is a measurement of the average kinetic energy of the molecules.
Temperature is a measurement of how hot or cold a substances is compared to a
standard scale.
3. When you touch a piece of metal and a piece of cloth (both at room temperature), which
one feels warmer? Colder? Why?
The piece of metal feels colder at room temperature than cloth because metal is a better
conduction, so it transfer heat away from my hand faster than the cloth.
4. Imagine we could magnify an object so much that we could see the atoms and
molecules.
a. If the object were cold, what would the atoms and molecules be doing?
If the object is cold, the atoms and molecules are moving slower (translational
movement).
b. If the object were hot, what would the molecules be doing?
If the object is hot, the atoms and molecules are moving faster (translational movement).
5. What kind of energy does a molecule have if it is moving?
Molecules have kinetic energy when it’s moving.
6. Which contains more energy: a cup of hot water at 90 or a pot of hot water at 90?
The pot of hot water will have more energy than a cup because more molecules will be
moving.
7. If you touch something and it feels hot, is energy being transferred?
Yes! Energy is being transferred from the object to me if I feel hot.
8. If you touch something and it feels cold, is energy being transferred?
Yes! Energy is being transferred from my body to the object if I feel cold.
9. Sometimes when a friend may not feel well, you may hold your hand to her forehead to
see if she has a fever. Why is this not the best way to check temperature?
Holding my hand in front of a friends’ forehead is not a good way to check temperature
because I can feel warmer/colder depending on the temperature of my hand.
10. What happens to the volume of most materials when they are heated?
When most materials are heated, the volume of the materials increase.
Summary of Heat Transfer: Complete the following table for heat transfer
mechanism and examples
Heat
Transfer
Heat
flows
from
Heat transmitted by…
Special
Features
Examples
conduction
hot to
cold
Contact of matter, or
through a material
Conductors
conduct heat
well. Metals are
good conductors
Sitting on
metal bench
in winter
Particles transfer energy
from one place to another,
but the particles don’t move
Convection
Hot to
cold
Fluids: gas or liquid (in
gravity field)
The particles of the warmer
material actually move –
warm fluid rises
Radiation
Hot to
cold
Insulators
conduct heat
poorly but they
do conduct
Depends on both
thermal
expansion and
buoyancy
Metal handle
of a pot on a
stove
Winds on
Earth (land
and sea
breezes)
Boiling water
in a pot
Light/Photons/Radiation/EM Everything emits
waves
and absorbs
radiation
No matter required
Dark colors
absorb and emit
well.
Hotter than
environment: net
emission; Cooler:
net absorption
Heat Lamp
Sunlight
Night side of
Earth has net
emission; Day
side has net
absorption