Thermal Flashcards
Define Internal energy (aqa definition)
The internal energy of a substance is defined as:
The sum of the randomly distributed kinetic and potential energies of the particles in a body
The symbol for internal energy is U, with units of joules
How can we determine high or low internal energy?
Particles are randomly distributed, meaning they all have different speeds and separations
The internal energy of a system is determined by:
-Temperature (higher temperature, higher kinetic energy and vice versa)
-The random motion of molecules
-The phase of matter: gases have the highest internal energy, solids have the lowest
-Intermolecular interactions between the particles
How do we change internal energy?
The internal energy of a system can increase by:
- Doing work on it
- Adding thermal energy to it (heating it)
The internal energy of a system can decrease by:
- Losing thermal energy to its surroundings
- The system doing work on its surroundings (e.g. a gas pushing a piston)
What is heat and how is it transferred?
Heat is the energy transferred from a body to another body due to a difference in temperature of the two bodies.
Heat is transferred FROM the hot body TO the cooler body.
If the body’s have the same temperature, there is no heat transfer so we say the bodies are in thermal equilibrium.
What is the first law of thermodynamics?
This is that the change in internal energy of a system is equal to the total energy transfer by doing work, or by heating.
Boiling point
Melting point
Boiling point is 100 degrees.
Melting Pont is 0 degrees.
Define specific heat capacity
The amount of thermal energy required to raise the temperature of 1 kg of a substance by 1 °C (or 1 K) without a change of state.
Specific heat capacity has the symbol c and is measured in units of Joules per kilogram per Kelvin (J kg–1 K–1) or Joules per kilogram per Celsius (J kg–1 °C–1)
Equation for SHC
ΔQ = mcΔθ
Different energy inputs for different substances
If a substance has a high SHC this means it takes long to heat up and cool down, as more energy is required to change its temperature. VICE VERSA
We can measure SHC using electrical methods, what is the equation for this?
Q=IVt
The Q is equal to m x c x change in t
We can use power to measure SHC, what is the equation?
Power = mass flow per second x SHC x Change in temp
Define latent heat
When a substance changes state, there is no temperature change
The energy supplied to change the state is called the latent heat and is defined as:
The thermal energy required to change the state of 1 kg of mass of a substance without any change of temperature
Define specific latent heat of fusion
The specific latent heat of fusion is defined as:
The thermal energy required to convert 1 kg of solid to liquid with no change in temperature
Latent heat of fusion applies to:
Melting a solid
Freezing a liquid
Define specific latent heat of vapourisation
The specific latent heat of vaporisation is defined as:
The thermal energy required to convert 1 kg of liquid to gas with no change in temperature
Latent heat of vaporisation applies to:
Vaporising a liquid
Condensing a gas
How can we see changes of state on a graph?
On a graph, of temperature of the y axis, and time on the x axis, the horizontal line shows the change of state taking place.
There is so change in temperature during the change of state and this is why the line is horizontal.
