Thermal physics Flashcards
Thermal equilibrium
when the rate at which 2 objects exchange thermal energy is zero which is when they are at the same temperature
2 fixed points on the Celsius scales are
melting point of ice: 0 degrees celsius
Boiling point of water: 100 degrees celsius
1 fixed point on the kelvin scale is
Absolute zero: 0K
Conversion between Celsius and Kelvin
Kelvin = Celsius + 273
Describe solids in terms of spacing ordering and motion
spacing: atoms are very closely packed
ordering: regular
motion: very slow and only vibration
describe liquids in terms of spacing ordering and motion
spacing: atoms are closely packed
ordering: random
motion: slow but atoms are free to move
Describe gases in terms of spacing ordering and motion
spacing: atoms are very far apart
ordering: random
motion: fast and atoms are free to move
describe the simple kinetic model of matter
the idea is that all materials can be modelled by considering the kinetic energy of the individual atoms and their collisions
describe how Brownian motion provides evidence for the kinetic model
smoke particles are inserted into a container of gas under a microscope
the smoke particles are seen to randomly change direction, due to the collisions with the invisible, small gas atoms
define internal energy
the sum of a systems kinetic energy and potential energy
relate internal energy to absolute zero
at absolute zero, a system is at minimum internal enegry
describe the relationship between internal energy and temperature
if temperature incresases, kinetic energy increases and therefore internal energy always increases.
however, if internal energy increases, that does not mean that temperature increases
Describe the energy transfers occurring during phase change and temperature change
before a phase change, thermal energy and electric potential energy are exchanged, resulting in a change in internal energy but no temperature change as kinetic energy is constant
during a temperature change, thermal energy and kinetic energy + electric potential energy are exchanged (materials expand/contracts as well as particle changing KE)
Define and calculate specific heat capacity
the thermal energy required to change the temperature of 1 kilogram of a substance by 1 degree.
c = Q / m∆T
describe an experiment to use an electrical method to determine specific heat capacity
(Set up a series circuit with a cell, voltmeter, heater and ammeter, with the voltmeter in parallel with the heater and the ammeter after.)
Measure the mass of the object using a mass balance
Make sure the material is insulated to ensure minimal heat is exchanged with the surroundings and measure the initial temperature with a thermometer. Turn on the heater, record the potential difference and current and measure the temperature every 30s. Plot a graph of temperature against time and find the gradient.
gradient = VI / mc
c = VI / m x gradient
define specific latent heat of fusion
the thermal energy required to change 1kg of a substance between a solid and a liquid
define specific latent heat of vaporisation
the thermal energy required to change 1kg of a substance between a liquid and a gas
calculate specific latent heat of vaporisation
L = Q / m
describe an experiment to use an electrical method to determine specific latent of a material
(Set up a series circuit with cell, voltmeter, heater, and ammeter, voltmeter being in parallel with the heater, and the ammeter after.)
Measure the mass of the material using a mass balance. Turn on the heater, measure the current and the potential difference and record the temperature every 30s until the material has completely changed state and the temperature has started to rise. calculate the time for which the material was at constant temperature and so was changing phase.
L = Q / m = VI / m
define Avogadro’s constant
the number of molecules of a substance in 1 mole. this is the same for every substance: 6.02 x 10^23
describe the assumptions made to model a gas using the kinetic model
the mass of the molecule is negligible compare to the container to allow the collision to be elastic and the molecule to keep all the kinetic energy . the volume of the molecule is negligible compare to the container so that the collision time is negligible compared to the time between collision. the molecules travel in a completely random way, obey the laws of Newtonian physics and the forces between molecules are negligible.
F = ∆mv / ∆t = 2mv / (2L/v) = (mv^2) / L
=> P = F / A = mv^2 / AL
explain how increasing the temperature of a gas at constant volume increases pressure
increasing the temperature increases the average kinetic energy of the molecules which means their r.m.s speed increases which increases the momentum change during the collision. since the cross-sectional area and length are constant, the increases in momentum change will cause an increase in pressure
explain how decreasing the volume of a container at constant temperature increases pressure
since temperature is constant, molecules r.m.s speed is constant and therefore the momentum change during the collision is the same. decreasing the volume will decrease both the area and also the time between collisions, both of which will act to increase the pressure.
state the ideal gas equation
pV = nRT
p: pressure
v: volume
n: number of moles
r: molar gas constant
t: temperature in kelvin
describe an experiment to investigate Boyle’s Law
measure the cross-sectional area of the syringe by using a micro meter to measure diameter and also measure the atmospheric pressure using a barometer and the initial gas volume. seal the end of the syringe by melting it and add a known masses to the block and record the new volume. Plot a graph of pressure against the reciprocal of volume which, if Boyle’s law is obeyed, will be a straight line through the origin.
describe an experiment to determine absolute zero
completely submerge a containers of gas in a water bath and connect a barometer to measure the pressure. measure the initial temperature with a thermometer and also the initial pressure. adjust the water bath to a higher temperature, allow time for the system to reach thermal equilibrium and record the new temperature and pressure. repeat the process at 5 more temperature and plot a graph of pressure vs temperature in Celsius.
state the equation of state and show how it is derived from the ideal gas equation
pV = NkT
k = R/Na
Nk = N(R / Na) = nR
=> pV = nRT
define mean square speed and relate it to pressure
the sum of the speed of individual molecules squared divided by the number of molecules. (Average speed squared)
describe the impact of temperature of root-mean-speed and the range of speeds of gas particles.
increasing the temperature increases the average kinetic energy/ r.m.s speed. increasing the temperature also increases the range of possible kinetic energies/ speeds the molecule can have.
