Chapter 3: Kinetic theory and thermal properties of matter

Question 1

State KPT

Answer 1

All matter is made of tiny particles called atoms and molecules. The particles are in constant random motion.

Question 2

What is brownian motion

Answer 2

Th haphazard movement of microscopic particles suspended in a fluid (liquid or gas). This is due to the uneven bombardment of the suspended particles by the molecules of the fluid.

• must be moving in straight lines until it hits something
• smoke particles are in constant random motion due to the uneven bombardment of unseen, fast moving air molecules

Question 3

Relationship between motion of the air particles and temperature

Answer 3

When temperature is higher, thermal energy is transferred and the air molecules gain kinetic energy. This causes the air molecules to move faster.

Question 4

Relationship between the motion of the air particles and the pressure of the gas

Answer 4

When randomly moving gas molecules hit the wall of the container –> they exert a force

pressure is defined as F/A, therefore the force acting on the wall gives rise to gas pressure.

Question 5

Explain what happens to gas molecules when thermal energy is transferred to gas

Answer 5

The gas molecules gain KE, move faster and collide with the piston @ higher speeds (or with a larger force/ more frequently) pushing it out.

Question 6

What is pressure law?

Answer 6

Pressure-temperature relationship:
- Pressure increases proportionally with absolute temperature
- Effect of rise in temperature for a fixed amount of gas and constant volume

P1/P2=T1/T2

Question 7

What is Charles’s law?

Answer 7

Volume-temperature relationship:
- Volume increases proportionally with absolute temperature
- Effect of the rise in temperature for a fixed amount gas and constant pressure

V1/V2 = T1/T2

Question 8

What is Boyle’s law?

Answer 8

Pressure-volume relationship:
- Pressure is INVERSELY proportional to volume
- Effect of the rise in volume for a fixed amount of gas at const. temp

(P1)(V1)=(P2)(V2)

Question 9

Expression for combination of 3 laws

Answer 9

PV/T

Question 10

Define internal energy

Answer 10

Sum of all the P.E and random K.E of all the particles in a substance

Question 11

State the effects of the change in the K.E and P.E of molecules

Answer 11

K.E:
- Absolute temperature
- a measurement of the average K.E of the molecules

P.E:
- Phase (aka state)
- Gaseous state has the largest P.E

Question 12

Define heat capacity

Answer 12

energy require to raise the temp of a substance by a unit temp (without a change of state)

C = Q/∆T
Q = C∆T

S.I unit = J K-1

Question 13

Define specific heat capacity

Answer 13

energy required to raise the temp of a UNIT MASS of a substance by a unit temp (without a change of state)

c = Q/m∆T
Q = mc∆T

S.I unit = J kg-1 K-1

Question 14

Specific heat capacity of water and ice

Answer 14

ice = 2100 J kg-1 K-1

water = 4200 J kg-1 K-1

Question 15

State changes in phase

Answer 15

melting
- MB weaken
- IMS increase slightly

freezing
- MB strengthen
- IMS decrease slightly

Evaporation
- more energetic surface molecules break bonds and escape
- ave KE of remaining molecules drop

Boiling
- MB broken
- IMS increase significantly

Condensing
- MB formed
- IMS decrease significantly

Question 16

State changes in phase for evaporation

Answer 16

Evaporation
- more energetic surface molecules break bonds and escape
- ave KE of remaining molecules drop

Question 17

Compare evaporation and boiling

Answer 17

Evaporation:
- @ surface of liquid
- @ all temps
- temp drops
- no bubbling

Boiling:
- throughout the liquid
- at fixed boiling point
- temp stays constant
- bubbling observed

Question 18

Factors that affect the rate of evaporation

Answer 18

1) Temperature
2) Humidity
3) Surface area
4) Motion of air (e.g wind)
5) External pressure
6) Volatility of liquid

Question 19

Comment about the energy needed to raise the temp of certain thing

Answer 19

Diff materials & same material but different mass –> diff. no. of particles, particles have different masses –> diff. amount of heat needed

Same material & mass or unit mass of same material (specific heat capacity) –> same no. of particles –> same amount of heat is needed

Question 20

Change of temp and change of phase

Answer 20

Change of temp = change in K.E of molecules

Change in phase = change in P.E of molecules

Question 21

Comment on heat needed to change phase for

Answer 21

Same substance, diff mass –> more mass requires more energy to change the phase

diff. substances, same mass –> diff. no. of and mass of particles diff. substances require diff. amount of energy

same substance, same mass. Does solid to liquid require more energy than liquid to gas?

Liquid to gas requires more energy as more energy is needed for the molecules to move further apart

Question 22

Define latent heat

Answer 22

Energy needed to change the phase of a substance (without change in temp)

Question 23

Define specific latent heat

Answer 23

Energy needed to change the phase of a UNIT MASS of a substance (without change in temp)

L = Q/m
Q = Lm
S.I unit = J kg-1

Question 24

Define specific latent heat of vaporisation (boiling and condensation)

Answer 24

Energy needed to change a unit mass from LIQUID to GASEOUS phase

Q = Lvm
S.I unit = J kg-1

Question 25

Define specific latent heat of fusion (melting and fusion)

Answer 25

Energy needed to change a unit mass from SOLID to LIQUID phase

Q = Lfm
S.I unit= J kg-1

Question 26

Specific latent heat of fusion and vaporisation of water

Answer 26

Fusion = 336 000 J kg-1

Vaporisation = 2 260 000 J kg-1