Physical Science
Thermal Energy and Heat
Name ________________________________
Period ____
These are the concepts that you are to know or demonstrate. I have given you sample questions that
could appear on your test to answer. Use the space provided to answer the questions.
1.
Understand the heating/cooling curve of substances
a.
For the following graph, properly label the where each state of matter exists and where the
melting and boiling points are on the graph.
(This is not water – melting pt ≠ 0°C and boiling pt ≠ 100°C)
Gas Phase
Boiling Point – where
liquid changes to gas
Liquid Phase
Melting Point – where
solid changes to liquid
Solid Phase
b.
Explain why there is no change in tempertature when there is a change in phase.
Any energy that is absorbed to go from solid to liquid or liquid to gas is used to break the particles away from each
other as opposed to giving the particles more energy (raise temperature). Likewise, energy released from particles as
they go from gas to liquid or liquid to solid is lost in order for the particles to change phase and become more ordered
instead of changing the energy of the particles (lowering the temperature).
c.
Does a cup of water boil at a different temperature than a large soup pot of water? Explain.
Boiling point for a substance is a physical characteristic of that substance no matter how much you have. Water will
always boil at 100°C – this is the amount if energy that is needed to change the liquid state of matter into a gaseous
state of matter. The amount of energy needed is never dependant on the amount of matter. It just may take longer
for the large soup pot to reach boiling.
2.
Understand the methods of heat transfer / Heat can only be transferred
between substances of different temperatures / Recognize the evidences that
indicate heat transfer / Know the difference between heat and temperature
a.
If you fill a cup with warm bathwater, will it contain more heat, less heat, or the same amount of
heat as the water remaining in the tub you just filled it from?
Both the bathwater and the cup are the same temperature. But temperature alone is not heat. Heat is temperature
AND mass of the matter. Since the bathtub contains more water particles and therefore more mass, the bathtub of
water will have more heat.
b.
What is the connection between heat and temperature?
Temperature is the measure of the kinetic energy of the particles in a substance. As long as particles are
moving, they will register some temperature (above 0 Kelvin). Heat is the measure of energy and the
amount of matter (temperature and mass of matter).
c.
At night, a rock in the desert will cool off. How could radiation, convection, and conduction
explain how the rock gets colder?
Since the rock is no longer receiving any of the radiation from the sun, it is no longer receiving energy for
the particles to absorb. The rock was warmed throughout the day via radiation and is warmer than the
surrounding air. When the air particles hit the rock particles, the rock particles will release some of its
energy to the air, thus decreasing the overall energy in the rock and increasing the air temperature nearest
the rock. Those warmed particles will move higher as they are less dense and cooler particles will replace
them thus creating convection currents, and the cycle continues with the transfer of energy.
d.
What substances make the best conductors, and what substances make the best insulators?
The best conductors are those where particles are tightly packed (solids) or where there is movement of
electrons from particle to particle that allows for the easy transfer of energy from atom to atom (metals).
The best insulators are where particles are not close together (gases) or where there are no free electrons for
energy to be transferred from particle to particle. Styrofoam, vacuum spaces and gases are good insulators.
e.
Why does heat energy always move from a higher temperature to a lower temperature?
All particles have energy – kinetic energy – when they are moving. When particles collide, those with
more kinetic energy will transfer some of their energy to those with less energy until all the particles have
the same energy. This is “equilibrium” = when everything is equal with energy. Really, they are not all the
same as some have a little more and some a little less, but overall, the amount of energy is within a small,
close range of each other.
f.
Know the difference between each of the three ways that energy is transferred and examples of
each.
Conduction = energy is transferred because of contact between particles. When particles of one thing touch
or collide with particles of another, this is conduction. (EX: pot on burner of stove, my cold hands holding
my husband’s warm hands). Convection = this occurs in fluids (gases or liquids) where warmer particles
will rise and cooler particles will take their place and get warmed, as a result there is a flow of warm and
cool particles. (EX: weather patterns due to unequal heating of air masses, currents in water as it boils,
ocean currents). Radiation = energy is transmitted via wavelengths so matter (solid, liquid or gas) is not
needed for the energy to be transmitted. (EX: sunlight, warmth from an incandescent light bulb).
g.
Discuss the difference between wool and cotton socks in the experiment that we did in class.
Cotton socks are not good insulators. The temperature of the water dropped more while the bottle was in the cotton
sock than the wool sock.
Wool socks are good insulators. The temperature of the water bottle dropped a little, but not as much as the cotton
sock. The heat energy lost to the environment (the calculation you did for Q) was a smaller value for the wool sock
than the cotton sock. That means if less heat was lost, more heat was held in and the wool is a better insulator.
h.
Does a melting ice cube warm its surroundings, cool its surroundings, or have no effect on its
surroundings? Why?
An ice cube will absorb energy from its surroundings (if the surroundings are a higher temperature than the ice cube)
and as that occurs, the loss of energy from the surroundings means that it is a cooler temperature. This is for those
few particles in the immediate area of the ice; however, since the air particles are greater in volume, we will not see
an over change in the air temperature due to a single ice cube.
i.
Do cold objects contain heat energy? Explain.
All particles that are at any normal temperature on Earth contain energy. As long as the particles are above 0 Kelvin,
particles contain energy and move/vibrate.
j.
How does a thermos work?
A thermos can keep hot things hot and cool things cool by its design. It is a container within a container and between
the two containers is a vacuum. The outer layer is plastic and therefore a poor conductor of energy. When the
energy of the particles on the outside cause the plastic to change in energy, the vacuum space slows the transfer rate
because there is no matter (no particles) to transfer the energy to the inner container. This allows the inner particles
to keep their energy either high or low as there can be no transfer of energy via conduction without matter present.
3.
Understand the kinetic molecular theory
a.
Why do substances expand when heat energy is added to them?
When energy is added to matter, the particles move or vibrate faster than they were previously. When particles move
faster, they take up more space. We see this every time you put a thermometer into a substance with greater energy
or when you heat metals (our demonstration with the ball and ring).
b.
Why is a Concord supersonic jet 8 inches longer in flight than when it is parked on the ground?
Metals, like liquids, expand when heated. So our question is really, what is heating the metal on the Concord so that
the metal expands? Friction is the answer. Friction between the air and the metal as the Concord moves very quickly
through the atmosphere is what provides the increased energy to the metal of the Concord to allow the metal particles
to expand and increase the size of the jet while in flight.
c.
If you don’t stir a liquid or a gas, then they are not moving…True or False? Explain your
reasoning.
False. All particles are in constant motion unless the particles are at 0 Kelvin. The only temperature in which
molecules stop moving is called Absolute Zero (0 Kelvin).
4.
Understand the concepts that surround absolute zero
a.
What is absolute zero?
Absolute zero is the temperature where all particles stop moving. We call it 0 Kelvin or -273.15°C. It is not
something we (humans) have gotten to (we’ve only gotten to -273.149999999°C). It is a value we’ve calculated
based on trends of how substances behave when cooled down.
b.
What is the coldest possible temperature? What does this temperature mean?
Absolute zero (0 Kelvin or -273.15°C) is the coldest temperature. It is when all particles of matter are to stop
moving and have no kinetic energy. It is a theoretical value as we have not achieved this temperature.
5.
Know how various heating & cooling appliances work
a.
Be able to explain a heating or cooling system in terms of their transfer of usable energy.
The refrigerator = You open the door and add items that were at room temp. The air in the fridge now comes in
contact with the cooling coils filled with cool liquid and the energy in the air is transferred to the liquid in the coils
thus cooling the air in the fridge and warming the liquid. The liquid passes through a compressor where the energy is
extracted and given to the air outside the fridge. The liquid passes through an expansion valve where the liquid now
has a cooler temperature to repeat the process within the fridge again.
6.
Measure temperature using different scales
a.
What is the difference between a thermometer based on a bimetallic strip and a mercury
thermometer?
A thermometer uses a liquid in a tube with a calibrated scale so that as the liquid heats up and expands, it is able to
measure the amount of kinetic energy of the surrounding particles (temperature), whereas a bimetallic strip is made
of two different metals that are adhered to each other so when heated, one metal expands more than the other causing
the metal strip to bend. This can also be made with a calibrated scale for the measuring of kinetic energy of the
surrounding particles.
b.
Know the difference between each of the three temperature scales… Why are there 3 different
temperature scales in use today?
Fahrenheit scale is used in the USA. It was derived using 0° as the temperature where ice and salt occur, 32° was the
freezing pt of water and there are 180° separating freezing from boiling water so boiling temp is 212°. Celsius scale
uses 0° as the freezing point of water and 100° separates freezing from boiling point. This scale is used worldwide,
except the USA. Kelvin scale is used in science and follows the deviations of the Celsius scale (100 divisions
separate freezing and boiling of water) but the 0 mark indicates no particle movement/energy so it never has negative
values for temperatures.
c.
How is temperature measured? (i.e. how do a thermometers work?)
Temperature measures the kinetic energy of the particles of whatever substance the thermometer is in. As
energy from the substance is transferred via conduction to the thermometer particles, the liquid particles in
the thermometer now move faster and expand (moves up the thermometer) until the energy of the liquid in
the thermometer is equal to the energy around the thermometer. If the environment is lower in energy, the
particles of liquid in the thermometer lose their energy to the environment, move slower, condense and the
liquid height in the tube goes down, indicating a lower temperature.