Thermal Properties of Materials Flashcards
Use the kinetic model of matter to describe the arrangement of particles in (i) solid (ii) liquid (iii) gas.
(i) Solid: The particles are packed closely together. Each particle is in close contact with all of its neighbours.
(ii) Liquid: The particles are packed slightly less closely together (compared with a solid). Each particle is still in close contact with most of its neighbours, but fewer than in solid.
(iii) Gas: The particles are widely separated from one another. They are no longer in contact, unless they collide with each other.
Use the kinetic model of matter to describe the movement of particles in (i) solid (ii) liquid (iii) gas.
(i) Solid: The particles vibrate about their fixed positions. They cannot move around because they are so tightly packed.
(ii) Liquid: Because the particles are slightly less tightly packed than in a solid, they can move around within the liquid. Hence, the particles are both vibrating and moving from place to place.
(iii) The particles are moving about freely, bouncing off one another and off the walls of their container.
Explain why a cooling effect accompanies evaporation.
When a liquid evaporate, the most energetic (fast-moving) molecules escape from the surface of the liquid. This leaves molecules with a below-average kinetic energy. Since temperature is a measure of the average kinetic energy of the molecules, the temperature of the evaporating liquid decreases. That is why a cooling effect accompanies evaporation.
Distinguish between evaporation and boiling.
- Evaporation can take place at any temperature. Boiling takes place at the boiling point.
- During evaporation, molecules escape from the surface of the liquid. Boiling takes place throughout the liquid.
Define specific heat capacity.
The energy required per unit mass to raise the temperature of a substance by one degree.
Define specific latent heat.
The energy required to change the state of unit mass of substance at constant temperature.
Define specific latent heat of fusion.
The energy required to change unit mass of solid to liquid at constant temperature.
Define specific latent heat of vaporisation.
The energy required to change unit mass of liquid to gas at constant temperature.
Define the internal energy of a system.
The sum of the random distribution of kinetic energy and potential energy of the molecules of a system.
Formula to calculate mean kinetic energy of a molecule.
mean kinetic energy = 3/2 kT
What is the relationship between mean kinetic energy of a molecule and the temperature?
Mean kinetic energy of a molecule is proportional to temperature.
State the first law of thermodynamics.
The increase in internal energy of a system is equal to the sum of heat supplied to the system and the work done on the system.
In the first law of thermodynamics, explain the meaning of the symbols:
(i) delta U
(ii) q
(iii) w
delta U: increase in internal energy of the system
q: heat supplied to the system
w: work done on the system
