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Physics > Thermal Physics > Flashcards

Thermal Physics Flashcards

1
Q

In what 2 conditions is energy transferred between 2 objects?

A

This occurs when one object does work on another or when one object is hotter than another object.In that case energy will be transferred by heating through convection and radiation.

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2
Q

What are the two possible ways in which the internal energy of an object can increase?

A

It can increase by work being done on the object or it can increase by heating that object.

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3
Q

When does internal energy remain constant?

A

This occurs when no work is done or no energy is transferred by heating.Or this can happen when the work done on the object is equal to the heat transferred from that object.

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4
Q

What is the first law of thermodynamics?

A

It states that the change in internal energy of an object=Difference in work done on object + energy transferred to object by heating-work done by object/

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5
Q

What is the internal energy of an object?

A

It is the sum of the random distribution of the kinetic and potential energies of its molecules.

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6
Q

What is thermal equilbrium?

A

This is where two objects are at the same temperature so no overall energy transfer by heating takes place.No net transfer of thermal energy

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7
Q

How to convert from temperature to kelvin?

A

degrees c=kelvin-273degrees.

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8
Q

What is absolute zero?

A

This occurs at 0k which is -273degrees.

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9
Q

What is the internal energy of an object at absolute zero?

A

The internal energy is minimum at absolute zero.

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10
Q

What is specific heat capacity?

A

It is the energy required to increase the temperature of a unit mass of a substance by 1k without a change in state.Units: Jkg^-1k-1

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11
Q

What happens to the potential and kinetic energies of particles during a change of state?

A

Potential energy changes because the position of the particles changes but ke remains constant.This is because energy is being used to break the bonds.Temp remains constant too.

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12
Q

What is specific latent heat?

A

It is the (thermal) energy required to change the state of a unit mass of a substance without changing its temperature.

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13
Q

What is the specific latent heat of fusion?

A

The energy required to freeze or melt an object.

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14
Q

What is the specific latent heat of vaporisation?

A

The energy required to boil or condense an object.

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15
Q

What is sublimation?

A

This when a solid directly turns into a gas.

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16
Q

What is boyles law?

A

It states that the volume of a fixed mass of an ideal gas at a constant temperature is inversely proportional to the pressure of the gas.

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17
Q

What is charles law?

A

This states that the volume of an ideal gas at constant pressure is directly proportional to the absolute temperature of that gas.

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18
Q

What is the pressure law?

A

Pressure law states that the pressure of an ideal gas at a constant volume is directly proportional to the absolute temperature of that gas.

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19
Q

Any change at a constant temperature is called what?

A

An isothermal change.

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20
Q

Any change at a constant pressure is called what?

A

It is called an isobaric change.

21
Q

Describe an experiment to test boyles law?

A

Use a cylindrical tube with a column of air trapped by oil.This should be connected to a bourdon gauge on top of an oil tank which is connected to a pump.Calculate the volume of the trapped air at atmospheric pressure by doing pixr^2xl length of the column of air.Increase the pressure on oil in the tank by using the pump and measure the length of the air column at regular intervals.Plot a graph of P against 1/v and it should give a straight line.Temp remains constant.

22
Q

Describe an experiment to test charles law?

A

Place a capillary tube containing a drop of concentrated sulfuric acid into a beaker.The acid should trap a column of air beneath it,use a ruler clamped behind the tube to measure the length of this column of air.Insert a thermometer into the beaker aswell.Pour boiling water into the beaker and measure the intial temp and the length of the air column.As the water cools measure the temperature of the water and the length of the column at regular intervals.After you have the results plot a graph of length against temp.This should be a straight line as V=pixr^2xL so l and v are both proportional to temperature.

23
Q

What is the molecular mass of a gas?

A

It is the mass of one molecule of that gas.Relative molecular mass is the mass of one molecule of a gas relative to carbon 12.It is the sum of the masses of all the atoms that make up that molecule.Sum of of the relative atomic masses.

24
Q

What is molar mass?

A

Molar mass is the mass of one mole of a gas and it is equal to the relative molecular mass of that substance.

25
Q

How to find the number of molecules in gas?

A

N=number of moles x avagadros constant

26
Q

What is the ideal gas equation?

A

pV=nRt.This equation works for gases at low pressures and fairly high temperatures.

27
Q

What is the equation of state aka the molecule ideal gas?

A

pV=NkT.Where k is Boltzmann constant and N is number of molecules.

28
Q

What is the work done in changing the volume of a gas at constant pressure?

A

It is p x delta v.

29
Q

What is the internal energy of gas molecules?

A

It is just the kinectic energy of the gas particles as there are no forces between them.

30
Q

What are the assumptions made in regard to the kinetic theory of gases?

A

All gas molecules are identical
Gas contains large number of molecules
molecules have negligible volume compared to container
Motion of molecules is random
Collisions between the wall and the molecules are perfectly elastic.
The molecules move in a straight line.
Ideal for low temp high pressure.

31
Q

What are empirical laws?

A

They are based on observations and evidence but cannot be explained using theory.The ideal gas laws are empirical.

32
Q

What is the ke of molecules at 0k?

A

it is zero

33
Q

What happens to gas particles when they are heated?

A

Their average kinetic energy increases and the average particle speed increases.The distribution of the speeds increases.

34
Q

Particles vs Atom vs Molecules

A

Atoms and molecules are types of particles.Molecules consist of one or more atoms.Atom is just a singular atom.

35
Q

What happens when a closed system is heated or work is done to it to transfer energy?

A

The internal energy of the system will increase and the average speeds of the particles will rise.

36
Q

Describe the continuous flow calorie meter expereiment?

A

Water flows in and is heated by a heating element the temp of the water is measured by the thermometer.The water passes over the heating element and then out through a hole where its final temp is measured.You can vary different values to see what impact it has on heating the water.Remember that the energy transferred to the water includes the heat lost to the surroundings.

37
Q

Is bond breaking endo or exothermic?

A

Bond breaking is endothermic as it requires energy to break bonds.Bond forming is exothermic as the reaction releases energy.

38
Q

What causes an increase in the rate of energy transfer between 2 objects?

A

A larger temp difference.

39
Q

Why is temp unchanged in freezing or condensation?

A

As thermal energy is released in the form of ke and potential energy rather than heat.

40
Q

What does an ideal gas follow?

A

It follows the 3 gas laws.

41
Q

Why are pressure and volume inversely proportional?

A

As the volume of a gas is reduced the particles are more compact together so they collide more frequently.

42
Q

What is avogadros constant?

A

It is defined as the number of atoms in one mole of a gas.It is 6.02x10^23mol^-1.

43
Q

How to find the molar mass of elements which are made up of 2 atoms?

A

Double their relative atomic mass to get their molar mass.

44
Q

Why does temp increase pressure when volume is constant?

A

If u increase temp of gas molecules their average kinetic energy increases and their average speed increases.This means that they will collide with the wall at a greater speed exerting a greater force on the wall which leads to a greater change in momentum.If volume is fixed the molecules will collide with each other more frequently.More collisions in a given time period increasing change in momentum

45
Q

If pressure remains constant when gas is heated?

A

Volume will increase the gas molecules will become more spread out.There will be a longer time between collisions and the rate of change of momentum will be reduced.

46
Q

What is kinetic theory based on?

A

Its based on theory and can be used to predict what happens and explain why it happens.

47
Q

What is brownian motion?

A

It explained the random motion of particles in a fluid.It was due to the collison of pollen grains/smoke particles with wather/air particles.Zig zag motion in fluids.

48
Q

Describe the understanding of gas lawes over time?

A

Boyles law-Pressure law-Charles law-Kinetic theory by assuming gas was made of tiny particles to explain boyles law.Brownian motion-Einstein.

Physics (19 decks)

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