PHY_10_V1_TG_Revision term 2 (1)

Thermal topics 3, 10

temperature, T [K]

measure of how hot something is (it can be used to work out the direction of the natural flow of thermal energy between two objects in thermal contact)

OR measure of the average K.E. of molecules

it is measured on a defined scale (Celsius, Kelvin etc.)

temperature is proportional to a measure of the average kinetic energy;

of the molecules of the substance;

  or:

idea that temperature shows natural direction of the flow of thermal energy;

from high to low temperature / OWTTE;  (do not accept ìhot to coldî) [2]

Award [1 max] for a rough and ready answer and [2 max] for a more detailed answer.

thermal energy

thermal energy is the KE of the component particles of an object thus measured in joules

heat, Q [J]

energy transferred from one body to another due to a temperature difference

thermal equilibrium

2 bodies that are in thermal contact are in thermal equilibrium when the net heat flow between them is zero, therefore the 2 bodies must have the same temperature

microscopic

on the scale of atoms and molecules

eg the microscopic properties of a gas are particle mass, velocity, kinetic energy, momentum

macroscopic

on the scale of people (ie what we observe)

eg the macroscopic properties of a gas are temperature, volume, pressure, density

ideal gas

gas that obeys the equation pV = nRT / no forces between molecules;

at all pressures, volumes and temperatures / any other postulate;

obeys the universal gas law / equation  or molecules are elastic spheres of negligible volume;

at all values of pressure, volume and temperature or no mutual force of attraction/repulsion;

satisfies pV = nRT (at all p, V and T) / point molecules / no intermolecular forces;

Allow any other kinetic theory assumption

kinetic theory of gases

a model of the microscopic behaviour of gas particles that explains the macroscopic behaviour of the gas (ie the ideal gas law, )

internal energy, U [J]

·         the sum of all random kinetic energies and mutual potential energies of the particles of the body or system

·         internal energy does not include the kinetic energy or potential energy of the body as a whole

·         an ideal gas has no intermolecular forces therefore the gas particles have no mutual potential energies therefore the internal energy of an ideal gas depends only on the KE of the particles (temperature of gas)

sum of (random) kinetic (and potential energies);

of the molecules of the system (allow atoms or particles);

mole, n [mol]

amount of substance of a system which contains as many elementary units as there are carbon atoms in 12 x 10^-3 kg of carbon-12

molar mass

the mass of one mole of a substance

Avogadro constant, N_A

the number of atoms in exactly 12 x 10^-3 kg of the nuclide carbon-12

specific heat capacity

c [J kg^-1 K^-1]

specific heat capacity is the amount of energy required to raise the temperature of unit mass through 1 K;

quantity of thermal energy (heat) required to raise temperature of unit mass;

by one degree;    

Award [1 max] for use of units, rather than quantities.

quantity of (thermal) energy/heat required to raise temperature of unit mass;

by one degree;

   or 

  with ,  and  explained;

Heat (thermal) capacity

C [J k^-1]

the amount of energy / heat required to raise the temperature of a substance / object through 1K/ C;

the energy/heat required to raise/change the temperature of a substance by1K/ C;

evaporation

evaporation is the escape of molecules from the surface of the liquid

boiling

boiling occurs when molecules escape in the form of bubbles of vapour from the body of the liquid

specific latent heat, l [J kg^-1]

energy per unit mass required to change the phase of a substance at its phase change temperature

specific latent heat of vaporisation: quantity of thermal energy/heat required to convert unit mass / mass of 1 kg of liquid to vapour/gas;

with no change of temperature / at its boiling point;

pressure, p [pascal, Pa]

the pressure experienced by a body immersed in a fluid is the (normal) force per unit area exerted by the fluid on the surface of the body

indicator diagram

graph of pressure against volume for a gas

isochoric (isovolumetric)

a process where the volume remains constant, therefore there is no work done ()

a process that takes place at constant volume

isobaric

a process where the pressure remains constant

a process that takes place at constant pressure

isothermal

a process where the temperature remains constant, therefore the internal energy remains constant for an ideal gas,

change in which the temperature stays constant;

adiabatic

a process where no heat enters or leaves the system,

a process in which there is no energy (heat) exchange;

between system and surrounding;

or

all the work done;

either increases or decreases the internal energy of the system;

a compression or expansion / change in state (of the gas);

in which no (thermal) energy is exchanged between the gas and the surroundings /

in which the work done is equal to the change in internal energy of the gas;

work (derivation)

force on piston = pA;

where A is area of piston.  Piston moves distance x;

work done = pAx;

Ax = V, so W = p V;

entropy,

S [J K^-1]

S [J K^-1], measure of disorder of a system

the degree of disorder (in the system)

2^nd law of thermodynamics

total entropy (of the universe);

is increasing;

in any process, (reaction, event etc.) the overall entropy of the universe/a closed system increases ;

total entropy of universe is increasing;