Thermal Energy Transfer COPY Flashcards
Define Internal energy
The sum of the randomly distributed kinetic and potential energies of the particles in a body.
Where does the electric potential energy that particles have come from?
The electrostatic forces that the particles exert on each other.
What is the first law of thermodynamics?
Heat supplied to a system = work done by system + increase in internal energy.
Heat supplied = (pressure x change in volume) + increase in internal energy
When will the work done by the system be positive?
If the material does work e.g. when a gas expands and pushes back the atmosphere
When will the work done by the system be negative?
If the gas contracts as then work is done on the gas.
When is the heat supplied to a system negative?
If heat energy leaves the substance
Define specific heat capacity
The heat energy required to raise 1kg of a substance through 1oC.
What are the units of specific heat capacity?
J/Kg/oC
What is the specific heat capacity equation?
Q = mc∆ø
How do you calculate heat gain/loss per second?
mass x SHC x temperature rise/loss per second
Why will the SHC of water that has been calculated from an experiment be too high? (3)
- Some heat will be lost to the atmosphere
- Some heat energy will be lost to the insulation and the thermometer
- Some heat energy will be lost due to the evaporation of the water and so will not cause the temp of the water to rise
What type of errors are heat losses?
Systematic
Why are heat energy losses systematic errors?
All the errors will cause the measured value for the increase in temperature to be too low
How can errors from heat losses be reduced? (3)
- Increasing the insulation of the calorimeter
- Use a thermometer with a thermal heat capacity which will not absorb the heat energy
- Start the experiment 5oC below RT and finishing 5oC above so that helf the time the water will absorb heat from the surroundings and half the time the water will release heat to the surroundings.
Define specific latent heat of fusion
The heat energy required to turn unit mass from solid to liquid at constant temperature
What are the units for specific latent heat of fusion?
J/Kg
What is the equation for specific latent heat of fusion?
Q = mLf
Define specific latent heat of vapourisation
The heat energy required to turn unit mass from liquid to gas at constant temperature
What are the units of Latent heat of vapourisation?
J/Kg
What is the equation for specific latent heat of vapourisation?
Q = mLv
Why doesn’t the temperature change when something changes state?
- The substance either loses/gains heat energy
- The Ek of the particles stays the same so the temperature doesn’t change
- The potential energy decreases (bonds form) or increases (bonds break)
Draw the cooling curve for stearic acid
What is the method to measure the SHC of water?
What is the theory behind the practical to measure the SHC of water?
- Assume no heat is lost from the calorimeter
- Energy supplied = energy supplied to calorimeter + energy supplied to water
- VIt = mcalCcu(ø2-ø1) + mwCw(ø2-ø1)
What is the method for measuring the temperature of a Bunsen flame?
- Measure the mass of the weight/nail/nut
- Measure the mass of the calorimeter
- Fill the tin can with 50 cm3 of water. Measure the new mass of the calorimeter to finf the exact mass of water
- Measure initial temp of water
- Heat the brass weight until it is red hot
- Drop the weight into the water and stir with a glass rod
- Measure the max temperature the water reaches
What is the theory behind the measuring the temerature of the bunsen flame practical.
- Energy lost by the brass weight when it enters the water and drops in temperature = energy gained by water from the nail which increases its temperature
