Thermal Physics Flashcards
What is the specific heat capacity (c) of a material?
The energy needed to raise the temperature of 1kg of the material by 1 degree Celsius/Kelvin without any change of state
What are the units of specific heat capacity (c)
J kg⁻¹ K⁻¹
How do you calculate the total energy supplied to an electrical heater.
W = IVt
What is the specific heat capacity of water?
4200 J kg⁻¹ K⁻¹
What is the specific latent heat of vaporisation (L) of a substance?
The energy required to change 1kg of a liquid to a gaseous state with no change in temperature
What is the specific latent heat of fusion (L) of a substance?
The energy required to change 1 kg of solid to liquid with no change in temperature.
What are the units of specific latent heat (L)?
J kg⁻¹
When would you use the equation ∆Q = mc∆T + mL?
If an object changes temperature and changes state during heating.
What is the internal energy of a substance?
The sum of the randomly distributed kinetic and potential energy of the particles in an object
What is thermal equilibrium?
When two objects at the same temperature so no heat flows between them.
What is the relationship between absolute temperature and the average KE of particles in a substance?
Absolute temperature is proportional to average kinetic energy of the particles in a substance.
What is the triple point of a substance?
The temperature and pressure at which a substance can exist in all three phases in thermal equilibrium.
Describe the kinetic model of a solid.
A regular arrangement of particles that are strongly attracted to each other. Particles vibrate around fixed positions.
Describe the kinetic model of a liquid.
Particles are attracted to each other but are able to move relative to each other (flow)
Describe the kinetic model of a gas
Particles are far apart and there are no forces of attraction between them. They occupy the volume of the whole container.
Why doesn’t the temperature of a substance change whilst it is changing state?
The electrostatic potential of the particles is changing rather than the kinetic energy
Why is the electrostatic potential energy of liquids and solids negative?
Energy must be supplied to the substance to break the bonds between particles.
What effect does increasing the temperature have on the particles in a substance?
t increases their average kinetic energy
What is Brownian motion?
The random motion of small particles such as pollen grains or smoke particles suspended in a fluid.
What causes Brownian motion?
The collisions between the individual atoms/molecules and the smoke/pollen particle transfer momentum
What is the conclusion from Brownian motion?
Particles that make up a fluid/gas are much smaller than the pollen/smoke particle and are in rapid, random motion.
What is Avogadro’s constant?
A number of particles equal to the number of atoms in 12 grams of carbon-12
What is one mole of a substance?
An amount in which the number of atoms/molecules is equal to Avogadro’s constant.
What is the molar mass of a substance?
The mass of one mole of a substance.
How do you find the mass of one atom from its nucleon number?
Multiply nucleon number by the atomic mass unit (u) in kg.
How is the atomic mass unit defined?
It is 1/12th the mass of a Carbon-12 atom
How do you calculate the number of particles from the number of moles of a substance?
Number of particles = number of moles × Avogadro’s constant
How do you find the molar mass of a substance from the molecular mass.
Molar mass = Molecular mass x Avogadro’s Number
How do you find the total mass of a substance from the number of moles?
number of moles x molar mass
How do you calculate the number of moles of a substance from the number of particles?
Number of particles÷Avogadro’s number
How do you find the molar mass of an element from its nucleon number?
Molar mass is equal to nucleon number in grams.
Boyle’s law: Pressure is inversely proportional to…
Volume for a fixed mass of gas at constant temperature
Charles’ law: Volume is proportional to…
Absolute temperature for a fixed mass of gas at constant pressure.
Gay Lussac’s Law: Pressure is proportional to…
Absolute temperature for a fixed mass of gas at constant volume
Avogadro’s law: Volume occupied by a gas is proportional to…
Number of particles/moles if pressure and temperature are constant.
How do you find absolute zero from a pressure temperature graph?
Extrapolate the line to find the x-intercept.
What is R in pV = nRT?
Molar Gas Constant
What is N in pV = NkT?
Number of particles
What is n in pV = nRT?
Number of moles
What is k in pV = NkT?
Boltzmann constant
What units of temperature should be used in the ideal gas equation?
Kelvin
What is the equation of state for an ideal gas?
pV = NkT OR pV = nRT
What is an ideal gas?
A theoretical gas that obeys the gas laws at all pressures and temperatures
What are the SI units of pressure?
Pascal (Pa or Nm⁻²)
What is the definition of pressure?
The force per unit area exerted normally to a surface
What is the relationship between root mean square speed of particles in a gas and absolute temperature?
rms speed is proportional √(absolute temperature)
Why does increasing the temperature of an ideal gas increase pressure?
Particles have greater kinetic energy so there is a greater rate of collisions and greater change in momentum per collision.
Why does increasing the volume of an ideal gas decreases pressure?
P=F/A. Force exerted decreases as the rate of collisions with the container decreases and the surface area increases.
According to Newton’s second law if a particle experiences a change in momentum…
There must be a force acting on the particle.
According to Newton’s third law if a container exerts a force on a particle…
The particle must exert a force on the container.
How do you calculate the mean square speed of gas particles from their velocity?
Square the magnitude of the velocity of each individual gas molecule and then take the mean average of these values.
How do you calculate root mean square speed of a gas?
Square the magnitude of the velocity of each individual gas molecule, take the mean average of these values and then take the square root.
Why is root mean square speed used instead of velocity?
Average velocity is zero.
What is N in pV = ¹/₃ N m (c)²
Number of particles
What is (c)² in pV = ¹/₃ N m (c)²
Mean square speed
What is ³/₂kT equal to?
The mean kinetic energy of one gas particle
What form is the internal energy of an ideal gas?
Purely kinetic (i.e. no potential energy)
Why is there no potential energy in an ideal gas?
Becuase there are no force between particles (except during collisions).
What is ³/₂NkT equal to?
Total internal energy of an ideal gas.
Kinetic theory assumption concerning volume
The volume of the particles in a gas is negligible compared to the volume of the container
Kinetic theory assumption concerning forces
There are no electrostatic forces between particles except during collisions
Kinetic theory assumption concerning motion
Particles are in continuous, rapid, random motion.
Kinetic theory assumption concerning collisions
The collisions particles undergo with each other and the container are all elastic
Kinetic theory assumption concerning time
The duration of collisions is negligible compared to the time between collisions
What is the relationship between absolute temperature and the average KE of particles in a substance?
Absolute temperature is proportional to average kinetic energy of the particles in a substance.
