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Module 5 - Chapter 14 - Thermal Physics - Coggle Diagram
Module 5 - Chapter 14 - Thermal Physics
Temperature
Triple point
One specific temperature and pressure where three phases of matter can exist in thermal equilibrium
No net energy transfer between phases
Thermal equilibrium
If an object is hotter, there is a net flow of thermal energy from the hotter object to colder
Objects reach thermal euqilibrium when there isn't any net flow of thermal energy between them - same temperature
Colder objects gets hotter and vice versa
0th law of thermodynamics - If two objects are each in thermal equlibrium with a thrid, then all three are in thermal equilibrium with eachother
Measuring
Scales
Celcius - based on freezing/ boiling point of water, however these temperatures change depending on atmospheric pressure
Absolute temperature (in Kelvin) uses triple point of water and absolute 0, lowest possible temperature
Change in 1K is the same as 1 degree
Kinetic model
Solid
Regular arrangement, molecules in fixed positions
Strong electrostatic forces of attraction
Molecules vibrate
Liquid
Irregular arragment, molecules are close together (greater mean separation than solids) by have more kinetic energy and can move
Molcules flow past eachother
Weaker electrostatic forces than in solids
Gas
Molecules have the most kinetic energy out of states, and are much further apart
Negligible electrostatic forces
Molecules move randomly with different speeds
Brownian motion
Constant motion - fluid particles are always moving
Random motion - fluid partiucles move in different direction
Zig zag motion - fluid particles change direction many times
Describes motion of larger particles which suggests motion of fluid particles
Density
In general, a substance is denser in solids is than in liquids
Water freezes into regular crystalline pattern where molecules are held slightly further apart than in random arrangement in water
Internal energy
Sum of randomly distributed kinetic and potential energy of atoms or molcules within the substance
Internal eneral at absolute zero is the sume of electrostatic potential energy only as particles have 0 kinetic energy
As you increase temperature of a body, average kinetic energy of molecules increases
Hotter the substance, faster the atoms in it move and greater the internal energy
State change
Energy transferred increases the electrostatic potential energy
Temperature stays constant until the state chane is complete
Gas - zero electrostatic potential energy
Liquid - negative electrostatic potential energy - energy must be supplied to break bonds
Solid - large electrostatic forces so large negative value of electrostatic potential energy
Specific heat capacity
Energy required per unit mass to chane the temperature by 1K
units:
Determining SHC
Measure the energy transferred from the heater to the substance (E=IVt)
Measure the mass using mass balance and change in temperature by thermometer
Temperature-time graphs
Plots a graph of temperature against time
is the gradient
Increase accuracy
Insulate substances to minimise energy tranferred to surroudings
For liquids, make sure to stir so temperature is uniform throughout
Method of mixtures
Known mass of two substances are mixted together
Record final temperature at thermal equilibrium
One SHC is known so the other can be calculated
Specific latent heat
Energy required to change the phase per unti mass while at constant temperature
SLH of fusion
substance changes from solid to liquid
Measure energy transferred to object using E =IVt
Thermometer should be used to ensure ice is at its melting point, it should be just starting to melt
Measure the mass of sbstance that changes phase
SLH of vapourisation
substance changes from liquid to gas
Often much more than SLH of fusion as there is a much larger different between internal energy of a gas and liquid than liquid and solid
Electric heater can be used with a condenser to collect and easure the mass of a liquid that changes phase
Phase change can occur the other way, when water freezes, energy is transferred to surroundings as internal energy of water in solid is less than liquid
Combining
Heating solid to melting point
Heating solid at constant temperature
Heating liquid to its boiling point
Boiling liquid at constant temperature
Total energy can be found by adding energy transferred in each section
