Thermal Energy Flashcards
Define Internal Energy
It is the sum of random distribution of kinectic and potential energies associated with the molecules of the system
Define Heat Capacity
it is the amt of TE required to raise a the temperature of a substance by 1K or 1
degree celsius
Define Specific heat capacity
It is the amount of thermal energy required to raise the temp of a substance of a unite mass by 1K or 1 degree celsius
Whats thermal requilibrium
- Same temp
- no net heat flow
Define Latent heat
amt of heat absorbed or released by a substance during a change of state without a change in temperature
define latent heat of fusion/vaporisation
it is the amt of thermal energy required to change a unit mass of substance from liquid to gaseous state/ solid to liquid state without a change in its temperature.
Define Boiling
its a process in which a substances changes from liquid to gaseous state without a change in temperature.
How come an object left to cool from gas to liquid have a change in temp
drop in temperature comes from the loss in average kinetic energies of the
particles as the liquid cools
How come an object left to cool from gas to liquid does not have a change in temp
heat loss comes from the loss in potential energies of the particles as bonds
form to hold the particles in more stable configurations when the liquid
changes into a solid
Describe melting process
Process 1 (PQ): The particles in a solid (eg ice above) are held together by strong
bonds and are tightly packed. The internal potential energy of a solid is lower than that
of a liquid. As thermal energy is absorbed, the particles vibrate faster about their fixed
positions. The increase in the average kinetic energy of the particles cause the
temperature to increase.
Process 2 (QR): The thermal energy absorbed is used to weaken the strong
intermolecular forces between the solid particles, such that the particles move out of
their fixed positions and are further apart. Only the internal potential energy of the
particles is increased, and hence temperature remains constant. The energy required
to melt the substance is known as latent heat of fusion.
Process 3: (RS): When all bonds are broken, the thermal energy absorbed causes the
internal kinetic energy of the particles to increase, and hence the temperature of the
liquid increases.
Whats latent heat of vaporisation
: The thermal energy absorbed is used to overcome the intermolecular
forces of attraction between the liquid particles, until there is negligible intermolecular
force between the particles, and allows the particles to do work against the
atmosphere. Only the internal potential energy of the particles is increased, and hence
temperature remains constant. This energy is known as latent heat of vaporisation.
Describe evaporation
The molecules in a liquid are in constant random motion at different speeds.
At the surface, energetic molecules that have sufficient energy to overcome
atmospheric pressure and the attractive forces of neighbouring molecules escape
into the atmosphere.
The less energetic molecules are left behind in the liquid.
The average kinetic energy of the molecules in the liquid decreases.
The temperature of the liquid decreases.
Hence, evaporation cools down a liquid (i.e. a cooling effect accompanies
evaporation).
Difference between boiling and evaporation (5)
(boiling first then evaporation)
Occurs at a particular temperature,
known as the boiling point
Occurs at all temperatures in liquid state
Occurs throughout the liquid
(bubbles form within the liquid)
Occurs at the surface of the liquid
(no bubbling)
Temperature of liquid remains constant Temperature of liquid drops
Energy source is required, e.g. a heater Energy source is not required.
(Energy comes from surrounding.
A quick process A slow process
