Chapter 14 Thermal Physics Flashcards
What is a triple point?
This is a specific temperature and pressure where a substance can be a solid or a liquid or a gas and exist in a thermal equilibrium. For water this means that the ice doesn’t melt, the water vapour doesn’t condense
What happens if a hot object is placed next to a cold object?
The net flow of heat is from the hot object to the colder object.
What is thermal equilibrium?
This is when there is no net flow of thermal energy between them so all the objects must be at the same temperature
How is a scale of temperature created?
Two points are defined and then the temperature of other objects can be positioned on this scale
What is the absolute temperature scale?
This is a scale where the two defined points are the triple point of water and the lowest possible temperature (absolute 0).
What is the SI unit for Absolute temperature?
Kelvin (K)
What is an increase of 1*K in Celsius?
Increase of 1*C
What is 0*C in kelvin?
273*K
What is the density of ice vs water?
Ice is less dense than water. This is very uniquie
What happens to atoms/molecules in a solid?
They pack together tightly because of strong electrostatic forces. All the atoms / molecules stay together in a fixed formation
What happens to the atoms/molecules in a liquid?
They are still close together but they can move further apart and can change position
What happens to the atoms/molecules in a gas?
The atoms / molecules are free to move apart and there is almost no forces of attraction between them. They move randomely
What does the spacing of molecules in a substance at different physical phases affect?
It affects the density
Why is water less dense as a solid?
Because it forms a regular crystalline structure
What is the density of a solid vs liquid (usually)?
Solids are far more dense
What is the internal energy of a substance?
It is the sum of the randomly distributed kinetic and potential energies of atoms or molecules within a substance.
What happens to the internal energy of a substance when it is heated and why?
The internal energy increases because more heat causes the kinetic energy of a substance to increase. The hotter a substance the more kinetic energy it has
How can the internal energy of a substance increase without an increase in temperature?
If the substance is changing state. The energy is increased because the electrostatic forces between the atoms / molecules is increased
What happens when a substance is heated so it starts to melt / vaporise?
The heat energy goes into breaking the electrostatic forces and not into kinetic energy. Once the forces have been broken, only then does the heat energy go into increasing the kinetic energy
What is the electrostatic potential energy in a gas?
Zero
What is the electrostatic potential energy in a liquid?
Negative
What is the electrostatic potential energy in a solid?
Very large negative
What is specific heat capacity?
It is the energy required to increase the temperature per unit of substance(1Kg) by 1*K
What is the specific heat capacity of water? is this high or low?
4200JKg^-1K^-1
This is exceptionally high
What is the equation to find the energy put into a substance?
E = mcΔθ E = Energy m = mass c = Specific heat capacity θ = temperature
How is specific heat capacity calculated?
It is calculated by using an emersion heater placed in the substance which is surrounded by insulator material. The energy into the substance is calculated using a volt meter and an ammeter. They are used to find the joules of energy transferred.
A thermometer is used to measure the change in temperature
The mass of the substance is weighed at the beginning
Then use the equation: c = IVt / mΔθ
What can the gradient of a temperature-time graph be used to calculate?
It can be used to calculate the specific heat capacity using the equation: c = Power / m x gradient
What is the method of mixtures?
To work out the specific heat capacity, mix two substances together and record the final temperature. If the SHC of one of the substances is known then the other SHC can be calculated. Use the equation:
mcΔθ = mcΔθ
What is specific latent heat?
This is the energy required to change the phase per unit of mass while at a constant temperature
What is the equation for specific latent heat?
L = E / M
What is the specific latent heat of fusion?
This is the specific latent heat when a solid turns to a liquid
What is the specific latent heat of vaporisation
This is the specific latent heat when a liquid turns to a gas
How is the specific latent heat of fusion measured and calculated?
By heating the solid version of a substance with a submersion heater and using E = IVt.
This is then divided by the amount of solid melted to get the specific latent heat
How is the specific latent heat of vaporisation measured and calculated?
This is done by heating a liquid and collecting the gas and measuring the mass of the gas by condensing it.
These equations are used: E = IVt and L = E / M
What are the conditions for standard values of specific heat capacity and specific latent heat for substances?
They are all at atmospheric temperatures
When working out the energy into a substance that is increasing in temperature and changing states what needs to happen?
Both the specific heat capacity and the specific latent heats need to be calculated and added together
