5.1 Thermal Physics Flashcards
Define thermal equilibrium between two objects
There is no net transfer of thermal energy between the two objects
What is absolute 0
0 kelvin
How do you convert from degrees celsius to kelvin
+273
Describe the structure of particles in a solid
-Particles are arranged in a regular structure and are closely packed together
-Strong electrostatic forces of attraction between them holding them in fixed positions
-They can vibrate so have some kinetic energy
Describe the structure of particles in a liquid
-Particles are more free than in solids so can flow past each other but still very close together
-Have more kinetic energy than solids
-Weak electrostatic forces of attraction between particles
Describe the structure of particles in a gas
-Have more kinetic energy than liquid and solid and are free to move
-Move with random motion
-Negligible electrostatic forces of attraction between particles unless if they collide with other particles or container wall
How can you investigate Brownian motion
Observe smoke particles or pollen grains in water under a microscope
Define internal energy
The sum of the random kinetic and potential energy of atoms/molecules in a system
What happens to the internal energy when a substance goes from solid to liquid or liquid to gas
-Kinetic energy remains constant
-Temperature remains constant
-Potential energy increases
What happens when you increase the temperature of a substance
-Average kinetic energy of particles increases
-Potential energy remains constant
What features of water makes it a good coolant
High specific heat capacity
Can absorb large amount of energy without a significant change in temperature
Define specific heat capacity
Energy required per unit mass to change the temperature of a substance by 1 kelvin
Describe an electric experiment to determine the specific heat capacity of a metal or liquid
-Set up a power supply in series with an ammeter, variable resistor and heater with voltmeter in parallel of heater
-Measure initial and final temperature of substance with thermometer
-Measure time taken with a stopwatch
-Measure current and p.d with ammeter and voltmeter
-Make sure the solid/liquid is insulated
-Liquid must be stirred to ensure it has uniform temperature throughout
-Calculate energy using E = IVt
-Calculate specific heat capacity, E = MCT
What does the graph of temperature against time look like
Straight line with positive gradient
What is another way of measuring specific heat capacity
-Measure the mass of 2 substances with mass balance and initial temperature of each with a thermometer
-Specific heat capacity of 1 substance will be known
-Mix substances together
-Measure final temperature when at thermal equilibrium
-Calculate specific heat capacity of 1 of the substance using MCT(1) = MCT(2)
Define specific latent heat of a substance
Energy required to change the phase per unit mass while at a constant temperature
When do we use specific latent heat of fusion and specific latent heat of vaporisation
Solid to liquid
Liquid to gas
Describe an electrical experiment to determine the specific latent heat of fusion
-Use a heating circuit to convert ice to water
-Use a thermometer to ensure the ice is at its melting point before the heater is turned on
-Measure p.d across heater, current in heater and time heater is switched on and calculate energy transferred to ice
-Measure the mass of ice that changes state with a mass balance
Describe an electrical experiment to determine the specific latent heat of vaporisation
-Use an electrical heater with a condenser to collect and measure the mass of the liquid that changes state
-Measure p.d, current and time
-Calculate energy and then calculate L
What are the five assumptions in a kinetic model
1.Large number of particles in random rapid motion
2.Particles have negligible volume compared to the volume of the gas
3.All collisions are perfectly elastic
4.Time of collisions is negligible compared to time between collisions
5.Forces between particles are negligible except during collision
Explain how pressure is exerted on a gas
-Particles collide with container wall and the container wall exerts a force on them, changing their momentum
-Total change in momentum is -2mu
-The atom exerts an equal but opposite force on the container wall
-Force = change in momentum/change in time where momentum = -2mu
-Large number of particles collide with wall and therefore a large force is exerted on the wall
-Pressure = Force / cross-sectional area
What is Boyles law
Pressure is inversely proportional to volume given constant temperature
PV = Constant
Explain why pressure must be changed slowly when investigating Boyles law
To ensure the temperature remains constant
What is the relationship between pressure and temperature
Pressure is directly proportional to temperature at constant volume
P/T = Constant
Describe how to investigative PV = Constant
-Use a pressure gauge connected to a foot pump and volume scale
-Pump the pressure to maximum
-Open the tap and close to decrease pressure
-Measure volume
-Plot a graph of P against 1/V
-Straight line through origin
Describe how to investigate P/T = Constant
-Use a pressure gauge connected to a round bottom flask in a beaker with water and heater underneath
-Measure temperature with thermometer and pressure at time intervals when heating water
-Plot graph of P against T
-Extrapolate graph
What does the gradient in PV against T graph show
nR
