M5.1 Thermal Physics

Question 1

what are the fixed points around Kelvin

Answer 1

Absolute Zero
the triple point of water

Question 2

define brownian motion

Answer 2

the random motion of small particles suspended in a fluid
both direction and speed

Question 3

describe an experiment to see brownian motion

Answer 3

smoke cell under a microscope using a glass reservoir and a layer of vaseline
smoke should appear to have random motion
air particles knock carbon particles around
air particles too small to see in microscope

Question 4

why does brownian motion happen

Answer 4

the larger particles suspended collide with the air particles which changes their velocities
proves gasses move freely and randomly

Question 5

what are the assumptions in brownian motion

Answer 5

Forces between particles are negligible except during collisions
collisions are perfectly elastic
time of collision is negligible
particles occupy a negligible volume
there are lots of particles in random motion

Question 6

define internal energy

Answer 6

the sum of all the kinetic and potential energy stored in all the particles

Question 7

define electrostatic potential energy

Answer 7

the energy due to the separation between molecules

Question 8

what are the factors that affect internal energy

Answer 8

temperature
state of matter
intermolecular forces

Question 9

define a mole

Answer 9

unit of substanec
1 mole is the amount of particles to make their atomic mass in grams

Question 10

what is molar mass

Answer 10

mass of one mole of a substance
mass/num of mols

Question 11

what are the assumptions made in kinetic theory of an ideal gas

Answer 11

molecules of negligible volume
collisions are elastic
cannot be liquified
has no interactions between molecules (except collisions)
obeys te gas laws

Question 12

boyles law

Answer 12

pressure ∝ 1/V
when temperature is constant
p*v = constant

Question 13

charles law

Answer 13

V∝T
when pressure is constant
V/t = constant

Question 14

pressure law

Answer 14

P∝T
p/t = constant

Question 15

what do the pressure laws combine to make

Answer 15

PV/t =constant
when only one mole that constant is the molar gas constant
PV/t = nR
Pv = nRt

Question 16

what are the microscopic properties of a gas

Answer 16

mass and speed

Question 17

what are the macroscopic properties of a gas

Answer 17

pressure and volume

Question 18

describe the kinetic model of a solid and what happens when heated

Answer 18

particles in a fixed ordered lattice
Vibrate around a fixed point
very small spacing between particles

vibrations amplitue increased when heated

Question 19

describe the kinetic model of a liquid

Answer 19

have translational kinetic energy
and slide past each other

Question 20

describe the kinetic model of a gas

Answer 20

particles very far apart
random brownian motion

Question 21

define potential energy

Answer 21

energy caused by the intermolecular force and the acceleration caused by it
(look at the video notes in the one note)

Question 22

while heating a substance how do the energies change

Answer 22

when not changing state KE increases much more than PE
When changing state KE constant PE increases lots

Question 23

how to reduce uncertainty when measring the temperature or calculating the SHC

Answer 23

stir the water regularly to even the temperatures
some energy may be transfered to the container which could be included in calculations

Question 24

why do we must use the Kelvin scale when in the equation pV = nRT

Answer 24

becuase when p or V tends to 0 T must also tend to 0
Kelvin is the scale where that is 0

Question 25

aparatus set up to measure pressure against temperature of a gas ina conical flask
how would you ensure results are accurate [4]

Answer 25

turn heat off and stir to ensure heat is evenly distributed
make sure that as much of the conical flaks is immersed in the liquid as possible
the tube is small compared to the volume of the flask
allow time for heat to conduct to the air

Question 26

why has all the helium particles not escaped the atmosphere over a long period of time [2]
previous about why some helium can escape

Answer 26

helium nucleus is an alpha particle so is “replenished” to the atmosphere through radiation
helium is also found in natural gas deposits underground

Question 27

figure above is a maxwell boltzman distribution
Use your knowledge to of kinetic theory of gasses to describe the shape of this distribution and explain why some helium is able to escape from earth

Answer 27

random motion and elastic collisions of particles
leads to distribution of KEs among particles
few will have very high velocities at the top end of the distribution
to escape have to be very far from the rms
hence very few will be able to escape