chapter 3 kinetic particle theory (kpt)

Question 1

describe the arrangement and movement of particles in solids.

Answer 1

the particles
1. are closely packed in a regular arrangement
2. vibrate in fixed positions

Question 2

describe the arrangement and movement of particles in liquids.

Answer 2

the particles
1. are closely arranged in clusters in random arrangement
2. slide & roll over each other while still in contact with one another

Question 3

describe the arrangement and movement of particles in gases.

Answer 3

the particles
1. are far apart in random arrangement
2. move randomly at high speeds, and collide frequently with one another

Question 4

describe the differences between evaporation & boiling. (3 aspects)

Answer 4

1. temperature: evaporation happens over a range (between melting & boiling point), but boiling only happens at a sharp temp. (boiling point)
2. where: evaporation happens at the surface of the liquid, but boiling happens throughout the liquid
3. bubbles: evaporation does not have bubbles, but boiling has bubbles

Question 5

pure substances will melt/ boil ________ temperature, and impure substances will melt/ boil ________ temperature

Answer 5

at a SHARP temperature; over a RANGE or temperature

Question 6

describe the effect of impurities on the melting point.

Answer 6

• it causes the melting point to be LOWER than the pure substance
• the melting proceeds over a temperature RANGE

Question 7

describe the effect of impurities on the boiling point.

Answer 7

• it causes the boiling point to be HIGHER than the pure substance
• the boiling proceeds over a temperature RANGE

Question 7

what are the factors affecting the rate of diffusion? (3 factors)

Answer 7

1. temperature
2. relative atomic mass (Mr)
3. gravity

Question 8

define ‘diffusion’.

Answer 8

diffusion is the (net) movement of particles from a region of higher concentration to a region of lower concentration until the particles are EVENLY distributed.

Question 9

describe and explain how temperature affects the rate of diffusion.

Answer 9

When the temperature of a liquid or gas is increased, the rate of diffusion also INCREASES (diffuses faster)
1. at a higher temp., the particles gain MORE kinetic energy
2. therefore they will be able to move around at HIGHER speeds from a region of higher concentration to a region of lower concentration until they are evenly distributed.

Question 10

describe and explain how relative molecular mass (Mr) affects the rate of diffusion.

Answer 10

At the same temperature and pressure, a substance with LOWER molecular mass diffuses FASTER than that with a higher relative molecular mass (inversely proportional).

Question 11

explain why when the pressure of a gas is increased, the volume DECREASES.

Answer 11

• Gases can be compressed EASILY because there are a lot of empty space between particles.
• When the pressure is increased, the gas particles are PUSHED CLOSER to each other and therefore volume decreases.

Question 12

explain why when the pressure on a solid is increased, there is almost NO change in volume.

Answer 12

• Solids CANNOT be compressed because there is very little space between particles.
• When pressure is increased, the particles CANNOT be pushed closer to each other, and therefore there is almost no change in volume.

Question 13

explain why a solid has MORE MASS than the same volume of gas.

Answer 13

• In solids, there is very little space between particles while for the gases, there are a lot of empty space between particles. [show difference]
• As such, for solids, there will be MORE particles in the same volume of space as compared to gases and so a solid has MORE mass than the same volume of gases. [link to the difference in mass]

Question 14

explain why a small volume of water produces a MUCH LARGER volume of steam.

Answer 14

• In water, there is little space between particles, thus there is A LOT of water particles in a small volume, while for steam, there are a lot of empty space between particles.
• As such, the particles in steam are FURTHER apart than the particles in water, and so a small volume of water will produce a much larger volume of steam.

Question 15

explain why a gas at constant pressure INCREASES IN VOLUME when it is gently heated, but a solid does not.

Answer 15

• The attractive forces between the particles in a solid are VERY STRONG.
• When a solid is gently heated, the kinetic energy of the particles increase and they vibrate faster.
• However, the average distance between particles DOES NOT INCREASE because the
  amount of heat is INSUFFICIENT to overcome the very strong attractive forces and so the volume of the solid does not increase.
• The attractive forces between the particles in a gas are very WEAK.
• When a gas is gently heated, the amount of heat is SUFFICIENT to overcome these very weak forces and the average distance between particles INCREASES a lot, causing the
  volume to increase.

Question 16

explain why does a liquid take the shape of its container but not a solid.

Answer 16

• A liquid can take the shape of its container because the particles in a liquid DOES NOT occupy fixed positions.
• They are able to roll and slide to fill the container.
• A solid does not take the shape of its container because the particles in a solid occupy fixed positions.

Question 17

explain why solid ice loses its shape when it melts.

Answer 17

• Ice has a fixed shaped because the particles in ice occupy fixed positions.
• As ice melts, the intermolecular forces between water molecules are WEAKENED such that the particles are sliding and rolling over each other and the shape of water is no longer fixed.

Question 18

explain why is a gas easier to compress than a solid.

Answer 18

• In solids, there is very little space between particles while for gases, there are a lot of empty space between particles.
• As such, gases are easier to compress as gas particles can move closer to each other easily while it is much more difficult for solid particles to move closer to each other.