Thermal Physics M.5

Question 1

Define thermal equilibrium

Answer 1

its when two objects which are in contact are at the same temperature and so there is no net energy transfer between them

Question 2

What properties does the Celcius scale depend on?

Answer 2

the freezing and boiling points of water

Question 3

What do we call the lowest temperature possible?

Answer 3

Absolute zero ( 0 K)

Question 4

What occurs to particles at absolute zero?

Answer 4

they have the minimum possible energy

Question 5

How do you change a temperature value in degrees Celcius into kelvins?

Answer 5

You add 273

T ( K ) ≈ θ ( ºC) + 273

Question 6

Describe the arrangement of particles within a solid

Answer 6

• particles vibrate in fixed positions in regular lattice
• particles held together by strong forces of attraction

Question 7

Describe the arrangement of particles within a liquid

Answer 7

• particles are constantly moving around
• free to move around eachother but are attracted to one another

Question 8

Describe the arrangement of particles within a gas

Answer 8

• particles are free to move around randomly
• no forces of attraction between them

Question 9

What is Brownian motion

Answer 9

the random movement of small visible particles suspended in a fluid due to collisions with smaller, randomly moving atoms/molecules of the fluid

Question 10

How can you observe brownian motion in a lab?

Answer 10

1. Put smoke in brightly illuminated glass jar and observe particles using a microscope
2. the smoke particles will appear as bright specks moving haphazardly from side to side , and up and down

Question 11

Define Internal energy

Answer 11

the internal energy of a system is the sum of the random distribution of kinetic and potential energies of its atoms and molecules

Question 12

What occurs to a substance when you heat it?

Answer 12

its temperature increases →thereby increasing the kinetic energy of particles within it → and so its internal energy increases

Question 13

What occurs to a substance when it changes phase?

Answer 13

its internal energy changes because the change of phase alters the bonds and therefore the potential energy of the particles

*there is no change in temp when there is a change of phase

Question 14

Define specific heat capacity

Answer 14

the specific heat capacity of a substance is the energy required to raise the temperature of 1 kg of a substance by 1°C

Question 15

State the equation for specific heat capacity

Answer 15

E=mcθ

E- the energy change (J)

m - mass (kg)

c- specific heat capacity (J kg¯¹ K¯¹ OR J kg¯¹ °C¯¹)

Question 16

Explain how you would determine that value of the specific heat capacity of a material

Answer 16

1. insulate the material being heated and use lids for liquids to reduce energy losses to the surroundings
2. use an ammeter to obtain the values for the current flowing in the circuit, a voltmeter for the pd across the heater and a stopclock to measure the time you’ve spent heating the materials then you can calculate the energy (E) ( E= VIt )
3. You then plug in your values into E=mcθ to calculate c

Question 17

triple point of water

Answer 17

the point at which water can exist as a solid , liquid and gas simultaneously

Question 18

Temperature

Answer 18

a measure of how hot or cold an object is and is re;ated to the kinetic energy of the particles in a substance

Question 19

Define specific latent heat

Answer 19

the energy required to change the state of 1 kg of a substance

Question 20

State the equation for specific latent heat

Answer 20

E=mL

E- energy change (J)

m - mass (kg)

L- specific latent heat ( J kg¯¹)

Question 21

Explain how you would determine the specific latent heat of a material

Answer 21

For a solid,e.g. ice :

1. Place a heater and equal masses of ice in two funnels above beakers
2. Turn on one heater for 3 minutes and record the energy transferred (E=VIt) during the 3 minutes. Dont turn the other heater- its there so that you can measure how much ice melts due to the ambient temperature of the room
3. After 3 minutes measure the mass of water collected in each beaker then subtract one from the other to get the amount that melted solely due to the presense of the heater
4. E=ml and plug in your values to get L

For a liquid

boil water in a distiling flask , condense the vapour given off and divide the energy transferred by the mass of the condensed water collected

Question 22

Explain the concept , ‘1 mole of substance’

Answer 22

1 mole of a substance contains 6.02x10²³ particles

(this number is known as the Avogadro constant , N**A)

E.g. one water molecule is composed of two hydrogren atoms and one oyxgen atom

hydrogren has an atomic mass of 1 and oxygen has an atomic mass of 16 therefore the mass of one mole of water will be 18g

Question 23

State the equation to find the number of particles present in a substance

Answer 23

N=nNA

N-no. of particles

n- the no. of moles

NA- Avogadro’s number

1 mole of a substance will contain N**A particles

n moles of a substance will contain nN**A particles

Question 24

Ideal gas

Answer 24

a gas that has internal energy only in the form of random kinetic energy

Question 25

State 3 assumptions of the kinetic model of gas

Answer 25

1. the particles move rapidly and randomly
2. there are negligible forces between particles except during collisions
3. all collisions are perfectly elastic ( kinetic energy is conserved)

Question 26

Pressure

Answer 26

the force acting perpendicular to an area

Question 27

mean square speed

Answer 27

mean value of the square of the velocity for a large no. of particles moving randomly in a gas

Question 28

root mean square (r.m.s) speed

Answer 28

its the square root of the mean square speed

Question 29

State what each variable in the equation of pV=1/3Nmc² represents

Answer 29

p= pressure (Pa or Nm¯²)

V- volume (m³)

N- number of particles

m- mass (kg)

c²- mean square speed