convection & condensation and evaporation

Question 1

how does convection work in an immersion heater?

Answer 1

• heat energy transferred from heater coils to water by conduction
• particles near coils get more energy so start moving around faster
• so there is more distance between them (less dense)
• hotter water rises above the denser, cooler water
• it displaces the colder water out of the way making it sink towards the coils
• cold water heated by coils and process continues

Question 2

what is condensation?

Answer 2

when a gas turns into a liquid

Question 3

how does condensation work?

Answer 3

when a gas cools, the particles in the gas slow down and lose kinetic energy, the attractive forces between the particles pull them closer together, if they get cold enough condensation takes place and the gas becomes a liquid

Question 4

what is evaporation?

Answer 4

when a liquid turns into a gas

Question 5

what needs to happen for evaporation to work?

Answer 5

• the particles need to be traveling in the right direction to escape the liquid
• the particles need to be traveling fast enough to overcome the attractive forces of the other particles in the liquid

Question 6

what happens when the fastest particles evaporate from the liquid?

Answer 6

the average speed and kinetic energy of the remaining particles decreases, so the temperature of the remaining liquid falls and the liquid cools

Question 7

how can the cooling effect be useful?

Answer 7

you sweat when you exercise or get hot, as the water from the sweat on your skin evaporates it cools you down

Question 8

how can the rate of evaporation be made faster?

Answer 8

• raising the temperature (higher average particle energy so more particles will have the energy to escape)
• making the density lower (the forces between particles will be weaker so more particles will have enough energy to overcome these forces and escape the liquid)
• increasing the surface area (more particles will be near enough to the surface to escape the liquid)
• increasing airflow over the liquid (air above liquid replaced more quickly so concentration in the air will be lower, lower concentration of an evaporating substance in air it’s evaporating into= higher the rate of evaporation)

Question 9

how can the rate of evaporation be made faster?

Answer 9

• making the temperature of the gas lower (the average particles energy in the gas will be lower so more particles will slow down enough to clump together and form liquid droplets)
• making the temperature of the surface the gas touches lower
• making the density higher (the forces between the particles will be stronger so fewer particles will have enough energy to overcome forces and will instead clump together and form a liquid)
• making the airflow less (the concentration of the substance will be higher and so the rate of condensation will be greater)

Question 10

what is convection?

Answer 10

when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them