Chapter 14 - Thermal Physics Flashcards
Define temperature
Level of hotness of an object
outline the Celsius scale
uses the melting and freezing point of water, under atmospheric pressure
outline the thermodynamic scale
triple point of water, 273.16K and absolute zero
converting between kelvin and Celsius
K = C + 273
what is thermal equilibrium
No net transfer of thermal energy between two objects or substances
electrostatic potential energy in solids, liquids and gases
weak in solids, max of 0J in gases
Brownian motion
particles exhibit random motion because of the collisions of other molecules, for example smoke particles in air exhibit Brownian motion showing air particles are much smaller than smoke particles and move erratically
Internal energy
Sum of randomly distributed kinetic and potential energies associated with the atoms or molecules which make up the substance
What happens to the KE and PE of a substance when heated
During state change, so melting, PE increases but KE stays the same, temperature also remains constant, because thermal energy is being used to break bonds
When a substance is heated but doesn’t change state, KE increases and PE is constant
Absolute zero
-273C or 0K where the molecules completely stop moving and has minimal internal energy.
Specific heat capacity with equation
energy required per unit mass (1kg) to increase the temperature by 1K, E=mcΔθ
Specific latent heat with equation
Energy required to change the state of a substance per unit mass at constant temperature, E=mL
What is the amount of a substance
mole
How to find amount of a substance
n = m/M where m is the mass and M is the molar mass
Assumptions for Kinetic theory of gases
VENCT
- Volume of gas atoms is negligible compared to the volume of the gas
- Electrostatic forces between atoms are negligible, except for when the atoms are colliding
- The gas contains a large number of atoms which move with random, rapid motion
- Collisions between atoms and walls are perfectly elastic
- Time taken for atoms to collide is negligible compared to the time between collisions
Explain how a gas in a container produces a pressure
- as the collisions between atoms and the walls are elastic, they rebound with the same speed they travel in at.
- this makes their change in momentum mv - (-mv)
- equal to 2mv
- As the change in momentum is equal to Ft
- the average force exerted on the wall is F = 2mv/t
- from newtons third law we know the wall will exert an equal force in an opposite direction
- The total pressure on the wall is equal to the sum of each collision between atom and wall, and the area of the wall
Boyle’s Law
For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume
Charles Law
For a fixed mass of gas at a constant volume, the pressure is proportional to temperature
Ideal gas equation
pV = nRT
how to find root mean square speed
- sum all individual velocities of atoms
- divide by number of atoms
- square root this value
r.m.s equation for pressure
pV = ⅓Nmc^2 where c is the r.m.s
What does the Maxwell-Boltzmann distribution show
number of molecules with each speed, against speed
what happens to the graph when temperature is increased
it gets shallower and wider
derive boltzmann constant (k) equation
- if k = R/Na where Na is avagrados number
- pV = NRT/Na
- pV = NkT
relation of KE and temperature
KE α Temperature (K)
derive equation for mean kinetic energy of gas molecules
- pV = NkT and pV = ⅓Nmc^2
- kt = ⅓mc^2
- 3/2kt = 1/2mc^2
- KE = 3/2kt
relation of KE and internal energy
KE α internal energy as we assume electrostatic forces are zero, there is no potential energy.
