5.1 Thermal Physics

Question 1

what is an absolute or thermodynamic scale of temperature?

Answer 1

an absolute or thermodynamic scale of temperature is independent of the properties of any specific substance, measured in kelvin

Question 2

how do you convert from degrees to kelvin?

Answer 2

(degrees value) +273

Question 3

how do you convert from kelvin to degrees?

Answer 3

(kelvin value) -273

Question 4

what is the triple boiling point of water? and what is it roughly in degrees?

Answer 4

the temperature at which water can exist as a solid, liquid or gas (around 0.01 degrees)

Question 5

what is absolute zero?

Answer 5

absolute zero (0K) is the theoretical temperature at which a substance has MINIMAL INTERNAL ENERGY

Question 6

why can you not ever have absolute zero?

Answer 6

nothing can have 0 internal energy

Question 7

what is thermal equilibrium?

Answer 7

objects in contact with each other at the same temp. are in thermal equilibrium, this means that there is no heat flow (net energy transfer) between them

Question 8

what is the motion of particles, spacing of particles and forces acting on particles in a solid?

Answer 8

• particles vibrate about fixed points
• particles very close together, high density (low mean separation)
• very strong intermolecular forces

Question 9

what is the motion of particles, spacing of particles and forces acting on particles in a liquid?

Answer 9

• particles can slide past each other
• mean separation is greater than solids (less dense)
• less strong intermolecular forces

Question 10

what is the motion of particles, spacing of particles and forces acting on particles in a gas?

Answer 10

• random, rapid motion in all directions
• high mean separation, particles not close together, not dense
• virtually no attractive forces except during collisions

Question 11

what is the defintion of brownian motion?

Answer 11

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

Question 12

how did Brown discover brownian motion in 1827? how can you observe brownian motion in a lab?

Answer 12

• put some smoke in a brightly illuminated glass jar and observe the particles using a microscope
• the smoke particles appear as bright specs moving haphazardly from side to side, and up and down

Question 13

what were the observations and conclusions from the brownian motion seen during the experiment?

Answer 13

• jerky, random movement due to the collisions with air particles meaning air particles are constantly moving
• amir molecules cannot be seen by the naked eye meaning they must be very small
• there must be a large number of particles

Question 14

what is internal energy defined as?

Answer 14

internal energy is defined as the sum of the randomly distributed kinetic and potential energies of all atoms or molecules within a system

Question 15

what is the relationship between average KE and temperature?

Answer 15

average KE is proportional to temperature

Question 16

what does kinetic energy relate to/represent?

Answer 16

due to the movement, in the form of vibrational motion (dependent on the mass and velocity of particles)

Question 17

what does potential energy relate to/represent?

Answer 17

stored in the bonds and the inter-molecular forces of attraction (measured by the mean separation of the particles)

Question 18

what is the total internal energy equation?

Answer 18

kinetic energies + potential energies

Question 19

what is thermal energy?

Answer 19

the component of a body’s internal energy due to its temperature, thermal energy can be supplied to a body by heating it

Question 20

what are on the axis of the Maxwell-Boltzmann distribution curve?

Answer 20

molecular speed on the x axis

no. of molecules with that speed on the y axis

Question 21

where must all the lines start on a Maxwell-Boltzmann distribution curve?

Answer 21

the lines must start from zero because no molecules have zero energy

Question 22

if you increase the temp. of something what happens to the internal energy?

Answer 22

because the KE increases, the internal energy also increases

Question 23

if you supply thermal energy to an object but its temp. remains constant what is happening?

Answer 23

its potential energy increases, KE stays the same (the speed of the molecules stays roughly the same)

Question 24

what is the definition for specific heat capacity?

Answer 24

the specific heat capacity, c, of a substance is the amount of energy needed to raise the temperature of 1kg of a substance by 1 kelvin (or 1 degree celius)

Question 25

what are the units for specific heat capacity?

Answer 25

JKg-1K-1

Question 26

what is the equation for change in thermal energy?

Answer 26

E = mcΔϴ where E = the change in thermal energy c = specific heat capacity Δϴ = change in temperature in K or degrees

Question 27

outline an experiment to determine specific heat capacity

Answer 27

- put an electric heater in a liquid and fully submerge it along with a thermometer - wrap the container of liquid with an insulator and use a lid to prevent heat loss to surroundings - you can stir the solution for even heating - to work out c use E = mcΔϴ and equate this energy to the energy in the power equation (E = power x time) - power = IV so energy = IVt - IVt = mcΔϴ so work out c by using c = IVt / mΔϴ

Question 28

what does increasing the temperature do to the Maxwell-Boltzmann distribution curve?

Answer 28

flattens the curve and the peak spreads out as the AREA UNDER THE CURVE IS FIXED, more molecules posses a higher average speed

Question 29

what does a straight line (of 0 gradient) mean on a time of heating/temp graph?

Answer 29

the object is changing phase e.g water melting or boiling

Question 30

what does a line (of constant positive gradient) mean on a time of heating/temp graph?

Answer 30

the object isn't changing phase, KE of molecules increases

Question 31

outline an experiment to determine the specific heat capacity of a metal block using the method of mixtures

Answer 31

- heat a metal block of known mass, Mb, up to a temp Tb - quickly transfer this block into a container containing a mass of water, Mw, at a temp Tw - the hot block will heat the water, measure the temp of the water once is has reached a steady value Ts (reached equilibrium) - the heat energy gained by the water is equal to the heat lost by the block so MwCwΔϴw = MbCbΔϴb - for Δϴ always use (T2 - T1) but remember to minus the side that has LOST energy

Question 32

what is the definition for specific latent heat of fusion?

Answer 32

the amount of energy required to change the phase or state of 1kg of a substance from a solid to a liquid

Question 33

what is the definition for specific latent heat of vaporisation?

Answer 33

the amount of energy required to change the phase or state of 1kg of a substance from a liquid to a gas

Question 34

what is the equation for specific latent heat of fusion/vaporisation?

Answer 34

E = mL where m = mass of the substance (the larger the mass of the substance the more energy it takes to change the state>

Question 35

outline an experiment to measure the specific latent heat of a solid or liquid

Answer 35

- put a heating coil/electric heater and equal masses of ice in two funnels above beakers - turn on one coil for 3 mins, record the energy transferred in the 3 mins using P = IV and P = E / T - don't turn on the other coil - it's there to act as a control so you can measure how much ice melts due to the ambient temp. of the room - at the end of the 3 mins measure the mass of the water collected in both beakers, subtract one by the other to get the ice that melted due to the electrical input then use E = mLf

Question 36

what is one mole?

Answer 36

one mole of any substance is the amount of substance that contains as many particles as exactly 12g of carbon-12, one mole of a substance will contain 6.02 x 10^23 particles

Question 37

what is the equation for no. of particles or molecules?

Answer 37

``` N = n x NA where N = no. of particles n = no. of moles NA = Avogadro constant (be careful with big N and little n) ```

Question 38

what is Avogadro's constant?

Answer 38

6.02 x 10^23

Question 39

what is an ideal gas?

Answer 39

an ideal gas is a gas that has internal energy only in the form of RANDOM KINETIC ENERGY

Question 40

when do real gases will behave like an ideal gas?

Answer 40

real gases will behave like an ideal gas if they are at low pressure and a temperature significantly above their boiling point

Question 41

what are the five assumptions when modelling the behavior of an ideal gas?

Answer 41

- the gas contains a large number of molecules in rapid, random motion - all collisions are elastic (KE is conserved) - negligible forces between particles except during collisions - the time for a collision to happen is negligible compared to the time between collisions - the particles occupy negligible volume compared to the volume of gas

Question 42

what is the formula for pressure? and what is the units?

Answer 42

pressure = force / area (measured in pascals)

Question 43

what is the value of atmospheric pressure?

Answer 43

around 100kPa, or 100,000 Pa (the reason you are not crushed due to this pressure is that there is an equal and opposite pressure inside your body, acting outwards, so the forces are balanced)

Question 44

what causes pressure? how does it work?

Answer 44

a gas in a container exerts pressure on the container walls due to collisions of gas molecules with the container walls

Question 45

what are the 3 gas laws?

Answer 45

- Boyle's Law - Charles's Law - The Pressure-Temperature Law

Question 46

what is Boyle's Law?

Answer 46

the volume of a fixed mass is inversely proportional to the pressure exerted on the gas, under conditions of CONSTANT TEMPERATURE pV = constant (p1V1 = p2V2)

Question 47

what does a pressure/volume graph look like (Boyle's Law)? and at different temperatures?

Answer 47

inverse square, curve with decreasing gradient, the higher the temp the further away the curve from the origin

Question 48

what does a pressure/ (1/volume) graph look like? and at different temperatures?

Answer 48

graph with line with constant positive gradient, at higher temps the gradient gets steeper

Question 49

outline an experiment to investigate Boyle's law

Answer 49

- you can investigate the effect of pressure on volume by setting up a pump connected to a air pipe to a tube with oil in it - the oil confines a parcel of air in a sealed tube with fixed dimensions, a tyre pump is used to increase the pressure, as the pressure increases the air will compress and the volume occupied by air in the tube will reduce - measure the volume of air when the system is at atmospheric pressure, then gradually increase the pressure noting down both the pressure and the volume of air, multiplying them together at any point should give a constant

Question 50

what is Charle's law?

Answer 50

the volume v of a gas is directly proportional to its absolute temperature, T, at CONSTANT PRESSURE V / T = constant

Question 51

what does a volume/temp pressure look like? (Charle's Law)

Answer 51

straight line because they have a directly proportional relationship

Question 52

what is the pressure-temperature law?

Answer 52

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

Question 53

what does a pressure/temp pressure look like? (pressure-temp law)

Answer 53

straight line because they have a directly proportional relationship

Question 54

what is always kept constant in all 3 gas laws?

Answer 54

mass of the gas

Question 55

how do you remember the 3 gas laws?

Answer 55

remember order of laws, 1/2/3 1 - temp constant 2 - pressure constant 3 - volume constant

Question 56

outline an experiment to investigate pressure and temp of a gas at constant volume and how you can determine a value for absolute zero

Answer 56

- as you want to keep VOLUME constant, heat a fixed mass of gas in a sealed flask at constant volume - the flask is placed in a water bath which is heated to different temperatures and the pressure at different temps. is recorded by looking at the reading on the pressure gage - plot a graph of pressure against temp. and either extrapolate the line back to give a rough estimation of absolute zero (where the line crosses the x axis) or work out the equation of the line (y = mx + c) and make y = 0 - note that the thermometer should not touch the sides of the container, make the water fully touch the entire flask but that the flask doesn't touch the bottom of the beaker

Question 57

if you combine all 3 gas equations what do you get?

Answer 57

pV / T = constant (this constant is dependent on the amount of moles used)

Question 58

what is the ideal gas equation?

Answer 58

``` pV = nRT where p = pressure in pascals V = volume of gas in m^3 R = molar gas constant T = absolute temp of gas in kelvin ```

Question 59

what is the mean square speed?

Answer 59

the mean square speed is the mean value of the square of velocity c for a large number of gas particles (atoms or molecules) moving randomly in a gas

Question 60

what is the root mean square speed (r.m.s)? and what does it tell you?

Answer 60

it is the square root of the mean square speed, it gives you the 'typical' speed of a particle in kinetic theory

Question 61

what is the equation that links pressure and volume to speed of the particles?

Answer 61

``` pV = 1/3 Nmc^2bar where p = pressure of gas in pascals V = volume of gas in m^2 N = number of particles m = mass of the particles c = speed of the particles ```

Question 62

what is the Boltzmann constant?

Answer 62

the Boltzmann constant, k, is a constant used when relating the temperature of the gas to the mean translational kinetic energy of the particles in the gas, it can also be thought as the gas constant for a single molecules

Question 63

when do you use pV = nRT and pV = NKT?

Answer 63

``` pV = nRT ---> for moles (n) pV = NKT ---> for no. of atoms/molecules (N) ```

Question 64

what is the Boltzmann constant equal to?

Answer 64

k = R / Avogadro's constant

Question 65

what two equations can you equate to show the relationship between the mean kinetic energy of a molecule of mass m, the mean square speed and the absolute temp?

Answer 65

0.5mc^2bar = 3/2kT

Question 66

what is the relationship between mean kinetic energy and the absolute temp for a molecule?

Answer 66

they are directly proportional

Question 67

what conclusions can we make from an ideal gas having mean kinetic energy directly proportional to its temp?

Answer 67

because an ideal gas has energy only in the form of of kinetic energy we can say internal energy of a gas is directly proportional to its absolute temperature