thermal physics

Question 1

describe the structure of a solid

Answer 1

particles are fixed in a uniform lattice, where particles vibrate around their fixed positions
they are held in position by strong forces of electrostatic attraction

Question 2

describe the structure of a liquid

Answer 2

particles are not fixed in position: they are constantly moving around but there are still some forces of attraction

Question 3

describe the structure of a gas

Answer 3

particles are free to move around with constant random motion. there are no forces of attraction between particles in an ideal gas

Question 4

define thermal equilibrium

Answer 4

no net transfer of energy; two bodies in thermal equilibrium have the same temperature

Question 5

what is the celsius scale?

Answer 5

uses the freezing + boiling points of water to make a temperature scale

Question 6

what is the kelvin scale?

Answer 6

also the thermodynamic scale does not depend on the properties of the substance

Question 7

what value is absolute zero in degrees?

Answer 7

-273 degrees

Question 8

convert degrees to kelvin

Answer 8

+273

Question 9

what occurs when you heat a solid?

Answer 9

particles gain kinetic energy and vibrate more vigorously
eventually they may break away from the structure + become free to move around
when this happens, the solid has melted into a liquid

Question 10

what occurs when you heat a liquid?

Answer 10

some of the particles gain enough energy to break away from other particles
particles that escape from the body of the liquid become a gas

Question 11

what occurs when you heat a gas?

Answer 11

molecules collide with the container- these collisions are responsible for pressure which a gas exerts on the container

Question 12

what is brownian motion?

Answer 12

particles move with random, zig zag motion

Question 13

how could we observe Brownian motion?

Answer 13

put smoke in a brightly illuminated glass jar and observe particles using a microscope
smoke particles appear as bright specs moving haphazardly from side to side

Question 14

how did Einstein prove the existence of atoms and molecules in the air?

Answer 14

randomly moving particles were hitting the smoke particles unevenly, causing this motion

Question 15

define internal energy

Answer 15

the sum of the kinetic and potential energy of particles within a system

Question 16

what is the relationship between kinetic energy and temperature?

Answer 16

directly proportional

Question 17

what is potential energy caused by?

Answer 17

interactions between particles and is based on positions relative to each other

Question 18

what happens to a substance when it’s heated?

Answer 18

temperature increases so kinetic energy increases and the internal energy increases

Question 19

what happens when a substance changes phase?

Answer 19

the energy from the heat is used to alter and break the bonds within the substance but not to raise the temperature. as a result, the kinetic energy of the substance remains the same but the internal energy changes in order for it to change phase

Question 20

define specific heat capacity

Answer 20

the amount of energy needed to raise the temperature of 1kg of a substance by 1 degree or 1 kelvin

Question 21

give the equation for specific heat capacity

Answer 21

E= mcT

Question 22

how could you measure the specific heat capacity of a solid or a liquid?

Answer 22

heat substance with a heater until there is a temperature change of 10K, recording the time taken to do this
attach an ammeter and voltmeter to heater to work out energy supplied using E=VIt
rearrange specific heat capacity equation to calculate c

Question 23

define the specific latent heat of fusion

Answer 23

the amount of energy needed to melt or freeze 1kg of a substance

Question 24

define the specific latent heat of vaporisation

Answer 24

the amount of energy needed to boil or condense 1kg of a substance

Question 25

what is the equation for specific latent heat?

Answer 25

E=mL

Question 26

how could you measure the specific latent heat of a solid or liquid?

Answer 26

place a heating coil and equal masses of ice in 2 funnels above the beakers turn on one heating coil for 3 mins- record energy transferred after 3 mins, measure the mass of water collected in beakers. subtract one from the other to get the mass of ice that melted solely due to presence of heater use L= E/m to find slh

Question 27

what 3 laws does an ideal gas obey?

Answer 27

Boyle's law Charles' law pressure law

Question 28

what is Boyle's law? give any supporting equations

Answer 28

at a CONSTANT TEMPERATURE, the pressure and volume of a gas are inversely proportional higher temp= further curve from the origin pV=constant

Question 29

what is the pressure law? give any supporting equations

Answer 29

at a CONSTANT VOLUME, the pressure of a gas is directly proportional to temperature. P/T= constant

Question 30

what is Charles' law?

Answer 30

at a CONSTANT PRESSURE, the volume of a gas is directly proportional to its absolute temperature

Question 31

what equation is given when you combine all 3 gas laws?

Answer 31

PV/T= constant

Question 32

what is the gas constant?

Answer 32

8.31 J/mol/K

Question 33

what is the ideal gas equation?

Answer 33

pV=nRT

Question 34

what is Avogadro's constant?

Answer 34

6.02x10^23

Question 35

what equation can be used to find the number of particles?

Answer 35

N = n x Na

Question 36

what equation can be used to find the Boltzmann constant?

Answer 36

k= R/Na

Question 37

how can you get the equation pV=nKT

Answer 37

combine N = n Na and K = R/Na Nk=nR substitute into pV=nRT to get pV=nKT

Question 38

what is the Boltzmann constant?

Answer 38

1.38x10^-23 J/K

Question 39

describe the motion of a gas in a container

Answer 39

- particles of the gas are free to move around with constant random motion - there are no forces of attraction according to Newton's 1st law - they continue to move with constant velocity until they collide with another particle

Question 40

what happens when a particle collides with a wall of a container?

Answer 40

a force is exerted on the box the box exerts an equal and opposite force Newton's 3rd law

Question 41

how can you calculate the force exerted by a particle on the wall of a container?

Answer 41

``` -using Newton's second law F= rate of change in momentum p=mu rebound = -mu so change in momentum=2mu forces by one particle = mass x velocity ```

Question 42

describe how pressure arises from gases in a container

Answer 42

- the combined force from many particles is much larger, so lots of particles will be colliding with each wall at any given moment - motion is random, collisions will be spread all over the surface of each wall - result is a steady, even force on all walls of the box= pressure

Question 43

give an equation found when combining kinetic energy and the ideal gas equation

Answer 43

pV=1/3Nmc^2

Question 44

describe the effect of increasing volume

Answer 44

frequency of collision decreases as particles have further to travel between collisions this decreases pressure

Question 45

describe the effect of increasing the number of particles

Answer 45

increases the frequency of collisions between particles and container this increases the pressure

Question 46

describe the effect of increasing mass

Answer 46

greater force is exerted on the walls of the container (F=ma) greater pressure

Question 47

describe the effect of increasing speed

Answer 47

greater change in momentum as p=mv this means a greater force is exerted F= change in momentum over time

Question 48

give the assumptions of the kinetic theory

Answer 48

- gas contains a large number of particles - particles move rapidly + randomly - collisions are perfectly elastic - volume of particles in negligible when compared to the volume of the gas - no forces between particles except in a collision - length of time involved in a collision is negligible compared to time between collision

Question 49

what name is given to a gas that obeys all assumptions of the kinetic theory?

Answer 49

an ideal gas

Question 50

what does the Maxwell-Boltzmann distribution show?

Answer 50

it shows how the speeds of molecules are distributed in an ideal gas

Question 51

as the temperature of a gas increases, what effect does it have on an ideal gas?

Answer 51

the average particle speed increases the maximum particle speed increases the distribution curve is more spread out as a result of collisions, energy will be transferred between particles some particles will gain speed in a collision whereas others will slow down

Question 52

between collisions, how would you describe the speed of the particles?

Answer 52

they travel at constant speed

Question 53

what equation is created when equating 1/3Nmc^2=NkT?

Answer 53

E=3/2kT

Question 54

what is the relationship between average kinetic energy and internal energy to the absolute temperature?

Answer 54

directly proportional a rise in absolute temperature will cause an increase in the kinetic energy of the particles, meaning a rise in internal energy