Heat and temperature Flashcards
describe solids
-regular pattern
-dense
-can only vibrate
-strong forces of attraction
Describe liquids
-weaker forces of attraction compared to solids
-can flow
-higher energy levels compared to solids
Describe gases
-little attraction between molecules
-least dense
what is condensation?
gas to liquid
In a temperature, time graph, the temperature doesn’t rise uniformly (flat bits), why?
there comes a point where they’re vibrating so violently, the bonds between them start to break down, and they begin to lose their solid structure. During this point – the melting point – the substance does not heat up. Temperature stays constant because all the energy is going into breaking the bonds between them, (not into making them vibrate more energetically).
In a temperature, time graph, the temperature doesn’t rise uniformly (flat bits), why?
there comes a point where they’re vibrating so violently, the bonds between them start to break down, and they begin to lose their solid structure. During this point – the melting point – the substance does not heat up. Temperature stays constant because all the energy is going into breaking the bonds between them, (not into making them vibrate more energetically).
Describe evaporation
Evaporation occurs when a few particles of a liquid escape from the surface to become a gas - even if the liquid as a whole isn’t at boiling point. It happens because different particles within a substance have different energies
how can evaporation be sped up?
-The temperature of the liquid is higher. That way it’s more likely that particles will have sufficient energy to escape.
-The surface area between liquid and air is larger. Again, it’ll make it more likely for a particle to reach the surface to escape.
-Airflow over the surface is greater. Greater airflow gets rid of any evaporated particles in the air over the liquid. In terms of diffusion, this creates a large concentration gradient
heat can be transferred in what methods?
conduction, convection and radiation
what is conduction?
This is where particles pass on kinetic energy to their neighbours without actually moving (vibrating doesn’t count as moving here!). This occurs mainly in solids.
what factors affect the rate of conduction?
-Temperature difference. Like we mentioned, the larger the difference, the faster the conduction.
-Material. Is it a metal or non-metal, is the material in a solid or liquid state?
-Surface area. A larger surface area means more particle collisions can occur so heat can be transferred faster.
what is convection?
This occurs when higher energy particles move to cooler regions, heating them up. It’s the main method by which heat transfer occurs in liquids and gases, since their particles are free to move. Heat is transferred by ‘convection currents’
what is convection?
This occurs when higher energy particles move to cooler regions, heating them up. It’s the main method by which heat transfer occurs in liquids and gases, since their particles are free to move. Heat is transferred by ‘convection currents’
how does convection work, using the radiator as a heat source?
-Air particles gain energy, move around more energetically, causing that pocket of air to expand. It becomes less dense, and so it rises.
-It moves up and away from the radiator (the heat source)
-As it does so, it cools, becoming denser and sinking.
-This creates a cycle of air flow in the room, known as a convection current, which allows all the air particles in the room a chance to be near the radiator at some point, to heat up.
Describe radiation
heat transfer is by emission of infra-red electromagnetic waves. This doesn’t need a medium to pass through. As with all EM waves, it can travel through a vacuum.
