Thermal Physics

Question 1

What is Internal energy of gas ?

Answer 1

The sum of the randomly distributed kinetic and potential energies of its particles

Question 2

Absolute temperature scale

Answer 2

K = C + 273
- 0k is lowest possible temperature that any object can theoretically have
(K - Kelvins + C - Celsius)

Question 3

What happens to the internal energy of a system when energy is transferred to it ?

Answer 3

Increases ( Visa Versa)

- average speed of particles increase

Question 4

How can (heat) energy be transferred between substances ?

Answer 4

by the collision of particles

Question 5

What is Specific heat capacity (C) ?

Answer 5

The amount of heat energy required to change 1kg of material by 1 Kelvin

• Measured in JKg-1K-1
• heating will result in a change of temperature
• kinetic energy

Question 6

Specific heat capacity formula

Answer 6

Q = mcΔt

heat energy = mass x SHC x change in temperature

Question 7

What is a Continuous Flow (Calorimeter) ?

Answer 7

A fluid flow continuously over a heating element. As its flows, energy is transferred to the fluid.

• Help measure the SHC (change the p.d)
• Q = mcΔt + H ( H is the heat lost to the surroundings)
• random error is fluctuations in temperature of the water flowing in and systematic error is thermometers may not be exactly calibrated

Question 8

What is Specific latent heat (L) ?

Answer 8

The amount of heat energy required to change the state of 1kg of material

• Measured in JKg-1
• heating will result in change of state
• potential energy

Question 9

Specific latent heat formula

Answer 9

Q =ml

heat energy = mass x SLH

Question 10

What are the types of SLH ?

Answer 10

SLH of fusion - solid/liquid transitions
- solid -> liquid = melting
- liquid -> solid = solidifying
SLH of vaporisation - liquid/gas transitions
- liquid -> gas = vaporising
- gas -> liquid = condensing

Question 11

What is change of state ?

Answer 11

when a substances changes between a solid, liquid and gas. (potential energy of particles changes)

• when the substances changes state, the temperature remains the same as kinetic energy of particles remain the same
• graph (temperature/internal energy)

Question 12

What is Boyle’s Law ?

Answer 12

ideal gas at a constant TEMPERATURE (K) the pressure and volume are inversely proportional

• p ∝ 1/V (pV = constant)
• graph (pressure/volume) - curve (don’t touch axis’s)

Question 13

What is Charles’s Law ?

Answer 13

ideal gas at a constant PRESSURE (Pa) the volume is directly proportional to its absolute temperature

• V ∝ T (V/T = constant)
• graph (volume/temperature) - straight line

Question 14

What is Pressure Law ?

Answer 14

ideal gas at a constant VOLUME (m^3)the pressure is directly proportional to its absolute temperature

• p ∝ T (p/T = constant)
• graph (pressure/temperature) - straight line

Question 15

Explain Boyle’s Law

Answer 15

• constant temperature = particles speed remain the same
• volume decreased = more collisions per second
• rate of change of momentum increases
• force increases = pressure increases

Question 16

Explain Charle’s Law

Answer 16

• temperature increases = particles move at a greater speed (more KE)
• to maintain constant pressure = volume must increase
• so longer journey between collisions between particles
• constant rate of change of momentum = constant force = constant pressure

Question 17

Explain Pressure Law

Answer 17

• temperature increases = particles move at a grater speed (more KE)
• to maintain constant volume = pressure must increase
• particles rate of change of momentum increases
• increases force (on walls) = increased pressure

Question 18

What is Molecular mass ?

Answer 18

the sum of the masses of all the atoms that make up a single molecule (relative atomic mass)
- e.g. C02 is 12+16+16 = 44

Question 19

What is the Avogadro constant (NA) ?

Answer 19

is the number pf atoms in exactly 12g of the carbon isotope 12/6 C

• 6.02 x 10^-23 mol-1
• at fixed volume of gas at a fixed temperature and pressure

Question 20

what is Molar mass of a substance ?

Answer 20

is the mass that 1 mole of that substance would have (equal to its relative molecular mss)
- e.g. helium is 4g because RAM = 4.0

Question 21

Calculate the number of molecules (N) in a substance ?

Answer 21

N = nNa

• number of molecules = number of moles x Avogadro constant
• number of moles measured in ‘mol’

Question 22

What is the ideal gas equation ?

Answer 22

PV = nRT
- combine the three laws -> PV/T = constant -> pV/T = nR
(pressure x volume = number of moles of gas x MOLAR GAS CONSTANT x Temperature)

Question 23

What is the Boltzmann Constant (k) ?

Answer 23

k = R/Na
(Boltzmann = Molar gas constant/Avogadro constant)
(Na = N/n) -> (Nk = nR) -> pV = NkT

Question 24

How to calculate WORK DONE on a gas ?

Answer 24

Work done = pΔV

• work done = energy transferred
• constant pressure - Charle’s law
• area under the graph =energy transferred to change volume of gas

Question 25

Derive the equation for the pressure exerted by an ideal gas ?

Answer 25

1) change in momentum -> mu - (-mu) = 2mu 2) time between collisions -> 2l/u (distance/velocity) 3) force -> mΔt/t -> 2mu/(2l/u) -> mu^2/l 4) pressure = F/A -> mu^2/l^3 -> mu^2/V (only for one particle) 5) N_u^2 = average 6) total pressure = mu^2/v = Nm_u^2/V _u^2 =1/3_c^2 EQUATION -> pV = 1/3 Nm_c^2 -> pV = 1/3 Nm (Crsm)^2 _c^2 = Crsm^2 = root mean square speed (typical speed)

Question 26

Assumptions made in 'kinetic theory' ?

Answer 26

- molecules act as point masses ( no volume) - all molecules of gas are identical - molecules continually move about randomly - molecules move in a straight line between collisions - time of collisions are negotiable (small) compared to time between collisions - collisions are perfectly elastic (between wall and particle)

Question 27

How to calculate the kinetic energy of gas molecules ?

Answer 27

1/2m(Crsm)^2 = 3/2kT = 3RT/2Na - equation made from ideal gas equation and kinetic theory equation - total kinetic energy - need to know number of molecules e.g. (1/2m(Crsm)^2) x n x Na

Question 28

What are Empirical Laws ?

Answer 28

are laws based on observations and evidence e.g. the gas laws including the ideal gas law. - the opposite it theoretical laws - based on theory (predicted and explained) e.g. kinetic theory

Question 29

How have the behaviour of gases have changed over time ?

Answer 29

at first the three gas laws were developed by a-lot of scientists - daniel BERNOULLI - explained Boyle's law

Question 30

What is the Brownian Motion ?

Answer 30

is the type of movement of any particles suspended in a fluid - provided evidence for the existence of atoms by noticing pollen grains in water moved with a zig-zag, random motion - helps the idea that everything is made from atoms