thermal Flashcards
internal energy
the sum of the kinetic energy and bond total energies of the molecules of a system as measured when the system as a while is not moving
thermal capacity
the amount of energy needed to raise the temperature of a substance by 1K
specific heat capacity
the amount of energy needed to raise the temperature of unit mass of a substance by 1K
specific latent heat
the amount of thermal energy needed to change the state of a unit mass of a substance at constant temperature
mole
the amount of a substance that contains the same number of atoms as 0.012kg of carbon-12
molar mass
mass of one mole of a substance
avogadro constant
the number of atoms in 0.012 kg of carbon-12 (approx 6x10^23)
pressure
the normal force to an area per unit area
temperature 2
1) a property that determines the direction of heat flow between two bodies in thermal contact
2) a measure of the average random kinetic energy of the molecules of an ideal gas
boiling point
temperature at which the vapor pressure of a liquid is equal to the pressure of the atmosphere on the liquid
whats the volume of 1 mole of any gas at normal atmospheric pressure & a temperature of 0*C
22.4 litres
difference between boiling and evaporation
boiling takes place throughout the liquid and always at the same temperature
evaporation takes place only at the surface of the liquid and can happen at all temperatures
how evaporation results in drop in temperature
when a liquid evaporates, the fastest-moving particles leave the surface
This means that the average kinetic energy of the remaining particles is lower, resulting in a drop in temperature
how does increasing the surface area lead to more evaporation
increases the number of molecules near the surface giving more of them a chance to escape
how does blowing across the surface increase the rate of evaporation
after molecules have left the surface they form a small ‘vapour cloud’ above the liquid. If this is blown away, it allows further molecules to leave the surface more easily
how does raising the temperature increase the rate of evaporation
increases the KE of the liquid molecules enabling more to escape
conduction 3
- takes place when bodies are in contact with each other
- the vibrating molecules of one body collides with the molecules of another
- the fast moving molecules lose energy and the slow-moving molecules gain it
the temperature of a gas in kelvin is directly proportional to
the average KE of a molecule
Boltzmann constant
1.38x10⁻²³J/K
Boltzmann constant
1.38x10⁻²³J/K
boyle’s law
the pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume
why is pressure of a gas inversely related to volume?
as the volume of a gas is reduced it will become denser, because the molecules are pushed together
The molecules will therefore hit the walls more often, increasing the rate of change of momentum and hence the pressure
pressure law
the pressure of a fixed mass of gas with constant volume is directly proportional to its temperature in kelvin
charles’ law
the volume of a fixed mass of gas at a constant pressure is directly proportional to its temperature in kelvin
why is volume proportional to temperature in kelvin at a constant pressure
as the temperature of the gas is increased the molecules move faster causing an increase in pressure
However if the volume is increased in proportion to the increase in temperature the pressure will remain the same
avogadros hypothesis
equal volumes of gas at the same temperature and pressure have the same number of molecules
why is there no potential energy in an ideal gas
since gas molecules have no force between them it requires no work to move them around which means that there is no energy associated with their position
2 ways of changing temperature
heating or doing work on the system
heat
energy transfer without the action of a macroscopic force
graphical representation of Boyle’s law
since the pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume, a graph of pressure against volume will be a curve
constant temperature
isothermal
constant volume
isochoric
constant pressure
isobaric
normal atmospheric pressure
101.3kPa
what conditions are needed for the ideal gas laws to apply to real gases
low pressure, large volume and high temperature
why is PE increased when molecules are squashed together?
bond energy increases
why do particles in an ideal gas need to be identical
different ones would have different masses which would change their acceleration
why do we assume a v large no of particles for an ideal gas
so results are statistically relevant - the average is more reliable with a bigger sample size
attractive force in solid
tension - as molecules pulled apart they push back
repulsive force in solid
normal reaction - as surfaces are pushed together the molecules push back
thermal equilibrium
when the rate of energy absorption is equal to the rate of energy emission
You know its reached when u keep on heating an object but its temperature remains constant
internal energy of an ideal gas
molecules of an ideal gas have only KE so internal energy is the total KE of the molecules
