Thermal Physics

Question 1

In what 2 conditions is energy transferred between 2 objects?

Answer 1

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.

Question 2

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

Answer 2

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

Question 3

When does internal energy remain constant?

Answer 3

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.

Question 4

What is the first law of thermodynamics?

Answer 4

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/

Question 5

What is the internal energy of an object?

Answer 5

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

Question 6

What is thermal equilbrium?

Answer 6

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

Question 7

How to convert from temperature to kelvin?

Answer 7

degrees c=kelvin-273degrees.

Question 8

What is absolute zero?

Answer 8

This occurs at 0k which is -273degrees.

Question 9

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

Answer 9

The internal energy is minimum at absolute zero.

Question 10

What is specific heat capacity?

Answer 10

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

Question 11

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

Answer 11

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.

Question 12

What is specific latent heat?

Answer 12

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

Question 13

What is the specific latent heat of fusion?

Answer 13

The energy required to freeze or melt an object.

Question 14

What is the specific latent heat of vaporisation?

Answer 14

The energy required to boil or condense an object.

Question 15

What is sublimation?

Answer 15

This when a solid directly turns into a gas.

Question 16

What is boyles law?

Answer 16

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.

Question 17

What is charles law?

Answer 17

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

Question 18

What is the pressure law?

Answer 18

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

Question 19

Any change at a constant temperature is called what?

Answer 19

An isothermal change.

Question 20

Any change at a constant pressure is called what?

Answer 20

It is called an isobaric change.

Question 21

Describe an experiment to test boyles law?

Answer 21

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.

Question 22

Describe an experiment to test charles law?

Answer 22

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.

Question 23

What is the molecular mass of a gas?

Answer 23

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.

Question 24

What is molar mass?

Answer 24

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

Question 25

How to find the number of molecules in gas?

Answer 25

N=number of moles x avagadros constant

Question 26

What is the ideal gas equation?

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

It is p x delta v.

Question 29

What is the internal energy of gas molecules?

Answer 29

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

Question 30

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

Answer 30

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.

Question 31

What are empirical laws?

Answer 31

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

Question 32

What is the ke of molecules at 0k?

Answer 32

it is zero

Question 33

What happens to gas particles when they are heated?

Answer 33

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

Question 34

Particles vs Atom vs Molecules

Answer 34

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

Question 35

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

Answer 35

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

Question 36

Describe the continuous flow calorie meter expereiment?

Answer 36

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.

Question 37

Is bond breaking endo or exothermic?

Answer 37

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

Question 38

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

Answer 38

A larger temp difference.

Question 39

Why is temp unchanged in freezing or condensation?

Answer 39

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

Question 40

What does an ideal gas follow?

Answer 40

It follows the 3 gas laws.

Question 41

Why are pressure and volume inversely proportional?

Answer 41

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

Question 42

What is avogadros constant?

Answer 42

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

Question 43

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

Answer 43

Double their relative atomic mass to get their molar mass.

Question 44

Why does temp increase pressure when volume is constant?

Answer 44

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

Question 45

If pressure remains constant when gas is heated?

Answer 45

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.

Question 46

What is kinetic theory based on?

Answer 46

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

Question 47

What is brownian motion?

Answer 47

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.

Question 48

Describe the understanding of gas lawes over time?

Answer 48

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