Kinetic Theory, Conduction, Convection, Evaporation, Condensation

Question 1

Explain arrangement and energy of particles in a solid?

Answer 1

Strong forces of attraction hold the particles close together in a fixed, regular arrangement

The particles don’t have much energy so they can only vibrate about their fixed positions

Question 2

Explain arrangement and energy of particles in a liquid?

Answer 2

Weaker forces of attraction between particles

Particles are close together but can move past each other, and form irregular arrangements

They have more energy than the particles in a solid - they move in random directions at low speeds

Question 3

Explain arrangement and energy of particles in a gas?

Answer 3

Almost no forces of attraction between the particles

Particles have more energy than those in liquids and solids - they’re free to move and travel in random directions at high speeds

Question 4

What is conduction of heat energy?

Answer 4

Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles

Question 5

What solids is conduction usually faster in? And why?

Answer 5

Denser solids

Because the particles are closer together and so will collide more often and pass energy between them

Question 6

What materials conduct heat slower?

Answer 6

Materials that have larger spaces between their particles conduct heat energy much more slowly - aka INSULATORS

Question 7

Why are metals good conductors?

Answer 7

Because their electrons are ‘free to move’ inside the metal

Question 8

What is convection?

Answer 8

Convection occurs in LIQUIDS AND GASES ONLY when the more energetic particles move from the hottor regions to the cooler region - and take their heat energy with them

Question 9

Explain how an immersion heater works?

Answer 9

• Heat energy is transferred from the heater coils to the water by conduction
• The particles near the coils get more energy, so they start moving around faster
• This means there’s more distance between them (i.e the water expands and becomes less dense)
• This reduction in density means that the hotter water tends to rise above the denser, cooler water
• As the hot water rises, it displaces (moves) the colder water out of the way, making it sink towards the heater coils
• This cold water is then heated up by the coils and rises - and so it goes on

→ You end up with convection currents going up, round and down, circulating the heat through the water

Question 10

Explain how a radiator creates convection currents

Answer 10

Heated, less dense air rises

Warm air dispaces cooler air

Cool, denser air falls

Cool air falls to fill the gap left by the rising, heated air

Question 11

Explain how condensation happens?

Answer 11

When a gas cools, the particles in the gas slow down and loose kinetic energy

The attractive forces between the particles pull them closer together

If the temperature gets cold enough and the gas particles get close enough together that condesation can take place and gas becomes a liquid

Question 12

In evaporation, particles near the surface can esacape and become gas if..?

Answer 12

• The partciles are travelling in the right direction to escape the liquid
• The particles are travelling fast enough (they have enough kinteic energy) to overcome the attractive forces of the other particles in the liquid

Question 13

The rate of evaporation will be faster if the…

Answer 13

• Temperature is higher - the average particle energy will be higher, so more particles will have enough energy to escape
• Density is lower - the forces between the particles will usually be weaker, so more particles will have neough energy to overcome these forces and escape the liquid
• Surface area is larger - more particles will be near enough to the surface to escape the liquid
• Airflow over the liquid is greater - the lower the concentration of an evaporating substance in the air it’s evaporating into, the higher the rate of evaporation. A greater airflow means air above the liquid is replaced more quickly, so the concentration in their air will be lower

Question 14

The rate of condensation will be greater if the..

Answer 14

• Temperature of the gas is lower - the average particle energy in the gas is lower - so more particles will slow down enough to clump together and form liquid droplets
• Temperature of the surface that the gas touches is lower
• Density is higher - the forces between the particles will be stronger. Fewer oartuckes wull have enough energy to overcome these forces and will instead clump together and form a liquid
• Airflow is less - the concentration of the substace in air will be higher, and so the rate of condensation will be greater

Question 15

Things that the rate of heat energy transfer depends on?

Answer 15

• Surfac area
• Volume
• Type of material
• If the materials in contact with insulators or conductors

Question 16

What the rate of heat energy transfer depends on: Surface area?

Answer 16

The bigger the surface area, the more infrared waves that can be emitted from (or absrobs by) the surface - so the quicker the transfer of heat

→ Many things (eg radiators, car engines, heat sinks) have increased surface areas so heat is radiated away quicker/maximined

Question 17

What the rate of heat energy transfer depends on: Volume?

Answer 17

If two objects at the same temperature have the same surface area but different volumes - the one with the smaller volume will cool more quickly as a higher proportion of the object will be in contact with its surroundings

Question 18

What the rate of heat energy transfer depends on: Type of material?

Answer 18

Objects made from good conductors transfer heat away more quickly that insulating materials (eg plastics)

Question 19

What the rate of heat energy transfer depends on: If the materials in contact with it are insulators or conductors?

Answer 19

It matters whether the materials in contact with it are conductors or insulators as if an object is in contact with a conudcotr - the heat will be conducted away much faster that if its in contact with a good insulator

Question 20

The ways products are designed to reduct heat energy transfers; vacuum flask? (explain)

Answer 20

• The glass bottle is double walled with a vacuum between the two wallks - this stops all conduction and convection through the side
• The walls either side of the vacuum are silvered to keep heat loss by radiation to a minimum
• The bottle is supported using insulating foam - this minimised heat conduction to or from the outer glass bottle
• The stopper is made of plastic and filled with cork or foam to reduce any conduction through it