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Physics > Section 8: Thermal Physics > Flashcards

Section 8: Thermal Physics Flashcards

1
Q

How is temperature measured?

A

Using the Kelvin (K) or absolute temperature scale

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2
Q

What is the lowest possible temperature that any object can theoretically have?

A

absolute zero
0K
-273 degrees Celsius

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3
Q

As the temperature of a gas increases, what happens the energy, speed and distribution curve?

A

The average kinetic energy of the particles increases.
The average particle speed increases.
The distribution curve becomes more spread out.

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4
Q

What is internal energy?

A

The internal energy of a body is the sum of the randomly distributed kinetic and potential energies of all its particles.

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5
Q

What is a closed system?

A

One which doesn’t allow any transfer of matter in or out. For a closed system, the total internal energy is constant, as long as it isn’t heated or cooled, and no energy is transferred to or from the system.

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6
Q

How does energy vary during collisions?

A

Energy is constantly transferred between particles within a system, through collisions between the particles. But the total combined energy of all the particles doesn’t change during these collisions.

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7
Q

What happens to the average speed of particles during collisions?

A

The energy of an individual particle changes at each collision, but the total internal energy of the system doesn’t change. So, the average speed of the particles will stay the same provided the temperature of the closed system stays the same and no work is done on the system.

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8
Q

How can internal energy of a system be increased and how does this change the average speed of the particles?

A

By heating it, or by doing work to transfer energy of the system (e.g. by changing its shape). In this case, the average speed of the particles will increase.

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9
Q

How can internal energy of a system be decreased and how does this change the energy of the particles?

A

The internal energy can be reduced by cooling the system, by doing work to remove energy from the system. In such a change, the average kinetic and/or potential energy of the particles will decrease as a result of energy being transferred from the system

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10
Q

What does specific heat capacity mean?

A

The specific heat capacity of a substance is the amount of energy needed to raise the temperature of 1kg of the substance by 1K

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11
Q

What is the symbol for specific heat capacity?

A

c

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12
Q

How do you find energy change using specific heat capacity?

A

energy change = mass x specific heat capacity x change in temperature

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13
Q
A
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14
Q

How can you use an experiment to investigate the factors that affect the change in temperature?

A

You can use this experiment to investigate how changing the mass of an object, changing the material the object is made from (and so changing the specific heat capacity) or changing the rate of energy transfer affect the change in temperature of that object. Decide which factor to investigate and keep all other unchanged. Then heat the water for a set amount of time and record the change in temperature. Repeat the experiment for different values of the factor you are changing, and compare the changes in temperature.

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15
Q

What is continuous-flow heating?

A

It is when a fluid flows continuously over a heating element. As it flows, energy is transferred to the fluid.

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16
Q

How can you find specific heat capacity using a continuous-flow calorimeter?

A

1 Set up the experiment and let water flow at a steady rate until the water out is at a constant temperature.
2 Record the flow rate of the water and duration of the experiment (to find the mass of water). You also need to measure the temperature difference (of the water from the point that it flows in to the point that it flows out) between the thermometers. Also record the current and potential difference.
3 The energy supplied to the water is Q=mcT +H, where H is the heat lost to the surroundings.
4 Repeat the experiment changing on the p.d. of the power supply and the flow rate (mass) so that change in temperature remains constant

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17
Q

What is a change of state and how does energy vary due to it?

A

It occurs when a substance changes between a solid, liquid or gas. When a substances changes state its internal energy changes bit its kinetic energy and temperature stays the same. This is because the potential energy of the particles is altered while the kinetic energy of the particles stays constant.

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18
Q

What is specific latent heat?

A

The specific latent heat of fusion or vaporisation is the quantity of thermal energy needed to be gained or lost to change the state of 1kg of a substance.

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19
Q

How does you find energy change using specific latent heat?

A

energy change = specific latent heat x mass of substance changed

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20
Q

What is the symbol of specific latent heat?

A

l

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21
Q

What is Boyle’s Law?

A

At a constant temperature, the pressure p and volume V of a gas are inversely proportional. It means that any given temperature, the product of p and V will always be the same.

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22
Q

What is an ideal gas?

A

It is a theoretical gas that obeys Boyle’s Law at all temperatures.

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23
Q

What is the Boyle’s Law practical?

A

1 The oil traps a pocket of air in a sealed tube with fixed dimensions.
2 Use a tyre pump to increase the pressure on the oil.
3 Use the bourdon gauge to record the pressure. As the pressure increases, more oil will be pushed into the tube, the oil level will rise, and the air will compress. The volume occupied by air in the tube will reduce.
4 Measure the volume of air when the system is at atmospheric pressure by multiplying the length of the part of the tube containing air by pi x radius of tube squared.
5 Gradually increase the pressure by a set interval, keeping the temperature constant.
6 Note down both the pressure and the volume of air it changes. Multiplying these together at any point give the same value.
7 Repeat the experiment twice more and take a mean for each reading.
8 If you plot a graph of p against 1/V, you should get a straight line.

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24
Q

What is Charles’ Law?

A

At constant pressure, the volume V of a gas is directly proportional to its absolute temperature T. If Charles’ law is obeyed, the volume divided by the temperature is a constant.

25
Q

What is the Charles’ Law practical?

A

1 For this experiment, you will need a capillary tube containing a drop of concentrated sulfuric acid positioned halfway up the tube. The tube should be sealed at the bottom, so that a small column of air is trapped between the bottom of the tube and the acid drop.
2 Place the capillary tube in a beaker of hot water. Position a ruler behind the capillary tube so that can measure the length of the column of air trapped between the bottom of the tube and the drop of sulphuric acid.
3 As the water cools, regularly record the temperature of the water and the length of the air column. You can assume the air pressure from the air above the droplet is constant.
4 Repeat the experiment with fresh bear-boiling water twice more, allowing the capillary tube to adjust to the new temperature between each repeat.
5 You should see that the length of the trapped air column decreases as the water temperature decreases.
6 Plot your results of length against temperature and you should get a clear straight line. This shows that the length of the air column is proportional to the temperature.

26
Q

What is the Pressure Law?

A

At constant volume, the pressure p of an ideal gas is directly proportional to its absolute temperature (T)

27
Q

How does the pressure law work in terms of particles?

A

If you heat a has, the particles gain kinetic energy. This means they move faster. If the volume doesn’t change, the particles will collide with each other and their container more often and at higher speed, increasing the pressure inside the container.

28
Q

What is molecular mass?

A

The sum of the masses of all the atoms that make up a single molecule

29
Q

What is the relative molecular mass?

A

The sum of the relative atomic masses of all the atoms making up a molecule.

30
Q

What is avogadros’s constant?

A

6.02x10 to the power of 23

31
Q

What is the definition of 1 mole?

A

A substance containing NA (Avogadro’s constant) atoms or molecules, all of which are identical.

32
Q

What is the molar mass of a substance?

A

The mass that 1 mole of the substance would have (usually in grams), and is equal to its relative atomic or relative molecular mass. For example, the molar mass of helium (relative atomic mass=4.0) is 4.0g

33
Q

What does the letter n mean?

A

the number of moles

34
Q

What does the letter N mean?

A

the number of molecules

35
Q

What is the molar gas constant?

A

8.31 JK-1mol-1

36
Q

What is the Boltzmann constant?

A

1.38x10-23 JK-1

37
Q

What letter represents the molar gas constant?

A

R

38
Q

What letter represents the Boltzmann constant?

A

k

39
Q

What must happen for a gas to expand or contract at a constant pressure?

A

work must be done - there must be a transfer of energy. This normally incolved the transfer of heat energy

40
Q

What does the area under a graph of pressure against volume show?

A

the energy transferred to change the volume of the gas

41
Q

What does rms speed stand for?

A

root mean square speed

42
Q

How is temperature related to the kinetic energy of molecules?

A

As temperature increases, the average speed of the molecules increases. This means the rate of change of momentum of the molecules colliding with the walls of the container increases, and so the force on the walls of the container increases

43
Q

If there is an increase in temperature and the volume of the container is fixed, why will the pressure increase? (2)

A

1 There will be more collisions between the molecules and the walls of the container in a given amount of time.
2 On average, a collision will result in a larger change in momentum, and so exert a larger force on the walls of the container.

44
Q

If the pressure inside the container remains constant and there is an increase in temperature, why the volume of the container will increase to compensate for the temperature change?

A

1 If the volume is larger, there will be a longer time between molecule-wall collisions, and so the rate of change of momentum and therefore the force on the walls of the container will be reduced.
2 As the volume increases, the surface area of the walls increases. Pressure is defined as force per unit area, and so increasing the area stops the pressure from increasing.

45
Q

What are the 8 assumption in the kinetic theory?

A

1 all molecules of the gas are identical
2 the gas contains a large number of molecules
3 the molecules are negligible volume compared with the volume of the container (they act as point masses)
4 the molecules continually move about randomly
5 Newtonian mechanics apply ( the motion of the molecules follows Newton’s Laws)
6 Collisions between molecules themselves or at the walls of a container are perfectly elastic (KE is conserved)
7 the molecules move in a straight line between collisions
8 The forces that act during collisions last for much less time than the time between collisions

46
Q

What type of gas obeys all of the assumptions about the kinetic theory?

A

an ideal gas

47
Q

What are real gases?

A

Real gases behave like ideal gases as long as the pressure isn’t too big and the temperature is reasonably high (compared with their boiling point), so they’re useful assumptions.

48
Q

What does the energy in ideal gases consist of?

A

For an ideal gas, you can assume that all the internal energy is in the form of kinetic energy.

49
Q

How do you find the total kinetic energy of the molecules in an ideal gas from the average kinetic energy?

A

Once you’ve found the average kinetic energy of the molecules in a gas, you can find the total kinetic energy of the molecules as long as you know how many there are. Just multiple the average kinetic energy by the total number of molecules present.

50
Q

What are empirical laws?

A

Empirical laws are based on observations and evidence. This means that they can predict what will happen but they don’t explain why. For example, the gas laws and the ideal gas equation are all based on observation of how a gas responds to changes in its environment.

51
Q

The kinetic theory is based on theory. What does this mean?

A

This means it’s based on assumptions and derivatives from knowledge and theories we already has, and will both predict and explain why a change will occur.

52
Q

Who discovered the relationship between pressure and volume at a constant temperature and when?

A

Robert Boyle in 1662

53
Q

Who discovered that the volume of a gas is proportional to temperature at a constant pressure and when?

A

Jacques Charles in 1787

54
Q

Who discovered the pressure law and when ?

A

Guillaume Amontons in 1699

55
Q

Who began the idea of the kinetic theory and when?

A

In the 18th century, a physicist called Daniel Bernoulli explained Boyle’s Law by assuming that gases were made up of tiny particles - beginnings of kinetic theory

56
Q

What discovered Brownian motion and when?

A

Robert Brown in 1827

57
Q

When was the kinetic theory widely accepted and why?

A

Most physicists thoughts it was just a useful hypothetical model and atoms didn’t really exist. It wasn’t until the 1900s, when Einstein was able to use kinetic theory to make predictions for Brownian motion, that atomic and kinetic theory became widely accepted.

58
Q

What is Brownian motion and how was it discovered?

A

In 1827, botanist Robert Brown noticed that pollen grains in water moved with a zigzag, random motion. This type of movement of any particles suspended in a fluid is known as Brownian motion

59
Q

How did Einstein use Brownian motion to support the kinetic theory?

A

Einstein showed that Brownian motion support the kinetic theory model of the different states of matter. He explained how the random motion of the pollen grains was a result of collisions with fast, randomly-moving particles in the fluid

Physics (16 decks)

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