Thermodynamics Flashcards
The total energy of all the atoms and molecules in an object.
Thermal Energy
Temperature
A measure of the average kinetic energy of the particles of a substance.
a temperature scale based on the freezing point of water at 32 degrees and boiling at 212 degrees.
Fahrenheit
“Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred.”
The First Law of Thermodynamics.
(By the way, the first law of thermodynamics is just a restatement of the law of conservation of energy)
The Third Law of Thermodyamics
“No system can reach absolute zero.”
(Believe me, they have tried)
(The problem is that you have to find somewhere for the last little bit of energy to go, and it will only go to someplace that is colder)
(You pretty much can’t ever find that place that is colder….)
Heat
Thermal Energy on the move.
(It has to be moving from one place to another to be considered “heat.”)
Joule
A unit used to measure energy. This is the SI unit.
Calorie
A unit used for measuring energy. This is the old unit of the English system and is still used in the United States.
Happens when the molecules of an object speed up and spread apart.
Thermal Expansion
The sum of the kinetic and potential energy of all the molecules in an object.
**Thermal energy **
(think kinetic and potential)
a temperature scale based on the freezing point of water at 0 degrees and boiling at 100 degrees.
Celsius
Absolute zero
The lowest possible temperature. The temperature at which the particles of an object have stopped moving completely. (You can’t go slower than stopped, so you can’t get any colder)
The second law of thermodynamics
Heat never spontaneously flows from a cold substance to a hot substance.
(In this context spontaneously means “by itself” or “without being forced” )
What is the definition of the word “heat?”
The thermal energy that is transferred from one object to another.
(Also known as “thermal energy on the move”)
Specific Heat Capacity
The quantity of thermal energy required to raise the temperature of a gram of some substance by 1 degree Celsius.
(It kind of tells you how hard or easy it is to heat something up)
(Water has an amazingly high heat capacity)
(That is why it takes a big lake until the late summer to heat up)
Thermal Energy
The total energy (kinetic plus potential) of the atoms and molecules that make up a substance.
(We typically just visualize the kinetic energy of the jiggling atoms and molecules, but it also includes some energy held in the bonds between atoms and molecules)
Thermal Expansion
When an object gets bigger (expands) because it gets hotter.
(When the particles jiggle more, they take up more space)
The bubbles you see forming in a pot of boiling water are made up of what?
A) Air
B) Water
C) Oxygen
D) Nitrogen
B
(If the bubbles were air, we would have to figure out where this air were coming from.
Are there little holes in the pot or something????)
(If the bubbles are made of water, we can explain that,
because the liquid water just turned into gaseous water, or steam)
Conduction
The transfer of heat energy by collisions between the particles in a substance.
(This is the primary mode of heat transfer in solids)
Melting
When a substance changes from the solid phase to the liquid phase
Is evaporation a heating process or a cooling process?
Cooling
(That is why your body sweats on a hot day)
When ice melts, does it absorb heat or give heat off?
It absorbs heat.
(You put ice in a cooler so that it can absorb the heat from your cans of soda pop. The ice absorbs the heat from the soda pop while the ice melts.)
Forced convection
When convection is made to occur with a fan or a pump.
(You probably have a “forced air” convection heating system in your home. Listen for the fan)
Natural convection
When convection happens because of differential heating of a fluid.
(In this context, “differential” means different parts of the fluid are at different temperatures)
(The heated air becomes less dense, then it rises. This causes all of the air to move, thus…convection)
In the thermal energy equation below, what does the “Q” stand for?
_Q_uantity of thermal energy
In the equation below, what does the “m” stand for.
The mass of the substance
In the thermal energy equation below, what does the “delta” stand for?
“Change in”
In this case, it works together with the “T” so that
delta T
means “change in temperature.”
In the thermal energy equation below, what does the “T” stand for?
“temperature”
Deposition
The change in phase directly from a gas to a solid.
the transfer of thermal energy in a liquid or a gas
(the particles containing the thermal energy actually move from one place to another.)
convection
the transfer of heat energy through direct contact
(the particles bump into each other and pass the energy from one to the next)
conduction
the transfer of energy by electromagnetic waves.
(this can transfer energy through empty space)
radiation
The three ways thermal energy can move from one place to another.
Conduction
Convection
Radiation
Boiling
Rapid evaporation that happens “within” a liquid.
(In this context, “within” means below the surface)
(This is why you can see bubbles)
Condensation
The change of phase from gas to liquid.
(You can see this in the summer when your can of pop “sweats.” The droplets of water are simply coming from the water in the surrounding air.)
Convection
The transfer of heat energy in a gas or liquid by means of currents in the gas or liquid. The fluid moves, and the thermal energy moves with it.
(Memory tool: Think _conve_ction - _conve_y - _conve_yor belt. Conveyor belts move objects from one place to another. Convection moves atoms and molecules from one place to another. The thermal energy goes with them.)
Evaporation
The change from the liquid phase to the gaseous phase.
Freezing
The change of phase from liquid to solid.
Heat of Fusion
The amount of thermal energy released when a substance changes from a liquid to a solid.
or
The amount of thermal energy absorbed when a substance changes from a solid to a liquid.
Heat of Vaporization
The amount of thermal energy released when a substance changes from a gas to a liquid.
or
The amount of thermal energy absorbed when a substance changes from a liquid to a gas.
Radiation
The mode of thermal energy transfer where the energy moves in electromagnetic waves.
(This is the only way thermal energy can move without matter being present)
Sublimation
The change of phase directly from the solid phase to the gaseous phase.
(This is what happened to the ice cream you left in your freezer for too long. The water in the ice cream went from solid ice straight to the gas phase. Most if it escaped the container, some re-crystalized upon what is left of the ice cream. The ice cream that is left is smaller, stickier, and icky.)
Does ice absorb or give off heat when it melts?
It absorbs heat.
(You put ice in your cooler so that it can absorb the heat in your can of soda pop)
(The ice absorbs the heat from the pop and melts)
If you want to melt ice, do you give it thermal energy or take thermal energy away from it.
You give it thermal energy.
If you want to freeze water, do you give it thermal energy, or do you take thermal energy away from it.
You take thermal energy away from it.
A) You put water in the freezer
B) Thermal energy flows from the water to the freezer compartment)
C) The water freezes.
When you melt ice, does it give off thermal energy?
No.
The ice absorbs thermal energy.
If you put ice in a hot pan on the stove, it melts faster because there is more thermal energy available for the ice to absorb.
What is the only thing you need to know to determine the direction that thermal energy will flow between two objects.
The temperature of each object.
(Thermal energy will flow from the high temperature object to the low temperature object.
What do you need to know to detemine if an object has a high or low average kinetic energy of its particles?
Temperature
What two temperature units are exactly the same size?
Kelvin and Celsius
Human body temperature is 98.6 degrees Fahrenheit. What is this in Celsius?
37 degrees Celsius
Which absorbs more solar energy, a white shirt or a black shirt?
Black shirt
Which reflects more solar energy, a white shirt or a black shirt?
white shirt
Water has a very high “specific heat capacity.” This is also known as _____________ _____________ because it describes how hard it is to change waters temperature.
Thermal inertia
Which is higher?
A) The melting point of water.
B) The freezing point of water
C) Both are the same.
C
Read carefully and really think about it…..
The amount of energy required to change 1 gram of a substance from a solid to a liquid, or from the liquid back to a solid.
Heat of fusion
The amount of energy required to change 1 gram of a substance from a liquid to a gas, or from the gas back to a liquid.
Heat of vaporization
A change directly from the solid phase to a gas phase.
Sublimation
(This is what is happening when “dry ice” disappears.)
Convection pretty much cannot happen in
A) Solids
B) Liquids
C) Gasses
A) Solids
The term “heat of fusion” is associated with a ____________ ______________.
phase change
(in this case, solid to liquid or liquid to solid)
The term “heat of vaporizaton” is associated with a ________________ _________________.
phase change
(in this case, gas to liquid or liquid to gas)
“internal energy” is another way to say ___________________
thermal energy
The particle model of matter says what about the motion of particles.
They are in constant motion
The particle model of matter says what about the composition of matter?
matter is made up of particles.
The particle model of matter says what about the forces between particles.
They are attracted to each other.
When water changes from a liquid to a solid, the particles move:
A) closer together
B) farther apart
C) stay about the same distance
B)
(This is why your can of Coke explodes when you leave it in the freezer too long)
P.S. - Water is pretty much the only substance that behaves this way.
What is the most awesome property of water?
It is the only substance we know of that actually expands when it changes from a liquid to a solid.
(Everything else gets smaller with it freezes)
Which is better at cooling things off.
A) Water evaporating
B) Water melting
A) Evaporating
(Water absorbs about 7 times as much energy when it evaporates as it does when it melts)
What term refers to the amount of energy you need to add to a solid to change it to the liquid phase or vise-versa?
Heat of Fusion
(Also known as Latent Heat of Fusion)
Which color of T-shirt will radiate the most thermal energy on a hot summer night, thus keeping you cooler?
A) Black
B) White
C) Both are the same
A) Black !!!
(The black shirt is most active as far as radiation is concerned. That means it will absorb the most thermal energy when the sun shines on it, and it will radiate the most thermal energy at night.)
Which temperature scale shows a temperature of “0” when the substance has absolutely no internal molecular energy?
Kelvin
Which of the following phase changes involve a release of heat energy from water?
Melting
Freezing
Boiling
Evaporating
Condensation
Sublimation
Deposition
Freezing (water releases heat energy into your freezer)
Condensation (when water condenses on your Coke can in the summer it releases heat energy into your Coke)
Deposition (Its like condensation and freezing both happening at the same time)
What detemines the direction thermal energy will flow between object “Z” and object “W” ?
The temperature of each object.
(If the temperature of “Z” is higher than the temperature of “W” then thermal energy will flow from “Z” to “W”.)
Heating
Movement of thermal energy.
A tiny rock has a temperature of 20 degrees celsius. You put it in a large bucket of water that has a temperature of 19 degrees celsius. Which way will the heat move?
Heat will move from the rock to the water.
The ONLY THING THAT MATTERS here is the temperature of the two objects. Heat flows from high temperature regions to low temperature regions.
What do the “contrails” streaming behind this jet have to do with what we are studying in science?
Contrail is short for “Condensation Trail.”
The hot air coming out of the jets is filled with moisture. When the hot moist air hits the cold air outside, the water condenses into little droplets that look like a cloud.
What is being shown here?
A convection current in water.
What do you add to matter to change its physical state?
You add thermal energy.
Below is a heat/temperature curve for a substance. What is the melting point of the substance?
- 50 degrees Celsius.
The horizontal parts of the graphs are phase changes.
Below is a heat/temperature curve for a substance. What is the freezing point of the substance?
- 50 degrees Celsius.
(Melting and freezing both happen at the same temperature. )
What happens to the density of a gas when it is heated?
The density decreases.
What happens to the volume of a gas when it is heated?
It increases.
What happens to the volume of a solid when it is heated
The volume increases.
What happens to the density of a solid when it is heated?
Its density decreases. (It becomes LESS dense)
What happens to the density of a liquid when it is heated and absorbs thermal energy?
It decreases. The liquid becomes LESS dense
What happens to the volume of a liquid when it absorbs thermal energy and gets hotter?
Its volume increases. (It takes up more space)
When we talk about the “absolute temperature” of an object, we are talking about its temperature on which scale?
(Fahrenheit, Celsius, or Kelvin)
Kelvin
If the absolute temperature of an ideal gas is doubled, the average kinetic energy of its molecules
