Thermal Physics Flashcards
Define absolute zero
The lowest possible temperature a substance can have, where there is no particle movement. -273°C or 0K
State the conversion equation from degrees Celsius to kelvins
K = C + 273
What happens to a particle’s average speed, average kinetic energy and distribution curve as temperature increases?
- As temperature increases, average particle speed increases
- As temperature increases, average particle kinetic energy increases
- The distribution curve is more spread out
Why is average speed and kinetic energy used for particles in a gas?
As the particles in a gas don’t all travel at the same speed
What is internal energy?
The sum of kinetic and potential energies of all a body’s randomly distributed particles
When do gases not have potential energy?
When the gas is an ideal gas
How can the internal energy of a system be increases?
- By heating the system
- By doing work to transfer energy to the sytem, i.e changing shape
In what direction is heat transfer?
- From hotter substances to colder substances
- The higher the difference in temperature between the substances, the faster the heat transfer
Define specific heat capacity
The amount of energy needed to raise the temperature of 1kg of the substance by 1K
When a substance changes state, what happens to its internal energy, kinetic energy, and temperature?
- Internal energy changes as potential energy of particles is altered
- Kinetic energy stays the same
- Temperature stays the same
Describe the graph of temperature against internal energy for a sample of water
- Constant gradient until 100°C as particles gain kinetic energy as water is heated
- Horizontal line as kinetic energy stays same while potential energy increases to break bonds
- Constant gradient past 100°C once water becomes vapour
Define specific latent heat
The amount of energy needed to change the state of 1kg of a substance
State Boyle’s Law
- At a constant temperature the pressure and volume of a gas are inversely proportional
- pV = constant
What is an ideal gas?
A gas which obeys boyle’s law at all temperatures
States Charles’ Law
- At constant pressure, the volume of a gas is directly proportional to its absolute temperature
- V/T = constant
Describe the graph of volume against temperature for an ideal gas at constant pressure on the degrees Celsius scale
- x axis = absolute zero = -273°C
- constant gradient
Describe the graph of volume against temperature for an ideal gas at a constant pressure on the kelvin scale
- x axis = absolute zero = 0K
- constant gradient
State the pressure law
- At constant volume, the pressure of an ideal gas is directly proportional to its absolute temperature
- P/T = constant
Define the Avogadro constant
The number of atoms in exactly 12g of carbon isotope
State the equation for the number of molecules
N = n(mol) x NA
State the equation the combination of the three gas laws give
PV/T = constant
State the ideal gas equation for n moles
pV = nRT
State the ideal gas equation for N molecules
pV = NkT
What is the conversion from litres to volume
1000 litres = 1m³
State the equation for work done for a gas to expand or contract at a constant temperature
Work done = p∆V
What does the area under a pressure-volume graph represent
The work done
What are the assumptions in kinetic theory?
- All molecules of the gas are identical
- The gas contains a large number of molecules
- Compared to the container, the molecules’ volume is negligible
- The molecules continuously move about randomly
- The motion of molecules follow newton’s laws
- Collisions between molecules themselves or walls of the container are elastic
- Between collisions, molecules move in a straight line
- Forces that act during collisions last for much less time than forces during collisions
What are empirical laws, giving an example?
Laws which are based of observation and evidence, i.e the gas laws
What are theories?
Predictions based on assumptions and derivations from knowledge and already developed theories, i.e Kinetic theory
Define Brownian motion
The motion of a visible particle suspended in a fluid being randomly affected by particles invisible to the human eye
What are the units for specific heat capacity?
J/KgK
When water turns to steam, what happens to its volume?
Volume increases 1000x as it expands
What is the specific heat capacity of water?
4200 J/KgK
State 6 assumptions of Brownian motion
- Collision between molecules themselves or between the molecules and walls of the container are perfectly elastic
- The time during a collision is negligible compared to the time between collisions
- The molecules continually move about randomly
- The molecules move in a straight line between collisions
- The molecules have a negligible volume compared to the volume of the container
- All molecules of the gas are identical
Define thermal equilibrium
No net transfer of thermal energy between objects
What is the potential energies of each state of matter?
- Solid = Low
- Liquid = Max
- Gas = 0, no bonds
What are the equations for number of moles?
- n = mass(g)/atomic mass
- n = mass(g)/molar mass
What is the equation for mass(kg) of atoms in a container involving molar mass(kg/mol)?
Mass(kg) = molar mass/NA where NA is Avogadro’s constant
