Kinetic Particle theory
They ask you what's matter? Simply answer that, 'matter is any substance that has mass and occupies space.'
Then matter exists in three states, we all know, solid, liquid, gas. And changes in temperature and pressure can result in changes in the states of matter.
Here they usually ask about the states of matter in a burning candle wax. Ans. Wax which is in a solid state of matter is melted by the heat of the flame and converts it to a liquid state of matter. The liquid wax is drawn up to the tip of the wick inside the flame. Here, the liquid wax is heated to an extent that it vaporizes into a gaseous state of matter.
Remember: Mercury is liquid at room temp and pressure.
· What is Kinetic particle theory? Ans. It states that all matter is made up of tiny particles and these particles are in constant, random motion.
Evidence? or Example?
· 'Dancing' dust in a beam of light. (can be seen)
· Smoke (can be seen + diffuses into air)
· Perfume - (link it to diffusion)
You should know about the properties of solids, liquids and gases. They are very simple, and you can find them in any book. I will just go through the small 'whys' regarding that. And they'll prolly sum that up.
Solids have a fixed shape and volume. why?
1. Particles have strong forces of attraction.
2. Therefore can't move about freely/held in fixed positions
3. They only have enough kinetic energy for vibrating or rotating in their fixed positions.
Liquids don't have a fixed shape. why?1. Forces of attraction (f.o.a) between particles liquid particles is weaker than solids.
2. Not held in fixed positions.
3. Arranged in disorderly manner
4. Can move about or slide over each other because less f.o.a means more Kinetic energy.
Liquids have a fixed volume. why?
1. Particles are farther away as compared to solids.
2. But still are closely packed. So can't be compressed. & have fixed volumes.
Gases have no fixed shapes nor fixed volumes. why?1. particles are far apart bcz f.o.a are very weak.
2. therefore particles have lots of K.E, & are not held in fixed positions.
3. Move in rapid random motion, bombarding into each other. so no fixed shape.
4. Lots of space b/w them, so easily compressed on applying of pressure/ they can be forced to move close together.
5. can be compressed so no fixed volume.
Remember: Always link these to Kinetic particle theory / Kinetic energy. It carries a mark.
You should know how to draw diagrams to show arrangement of particles in solids liquids and gases.
Changes of states occur. How?By temp change. during heating or cooling of a matter, the heat taken in, or given out causes the kinetic energy of a substance to change. And change in state occurs.
(The basic thing is that energy can change its form so the provided heat energy can turn into kinetic energy. when kinetic energy increases, f.o.a decrease, and particles move away. And vice versa).
Melting
Substance's state changes from solid to liquid. How?1. heat absorbed, converted to K.E, particles gain K.E, start vibrating faster at fixed positions.
2. At certain temp, vibrations overcome f.o.a and particles break away from fixed positions.
3. slide over each other, substance is now liquid.
This certain temp at which a substance changes from solid to liquid is the melting point.
Here is a question. Glucose has a melting point of 142 degree C. The melting point of glucose cannot be determined if you heat glucose in a test tube in water bath. Why? Ans. Water will heat up to 100 degree C only. However to melt glucose we require 142 degree C. Therefore glucose will not melt. So we can’t determine its melting point.
Freezing
Substance's state changes from liquid to solid. How?
1. Energy given out, or heat lost, particles lose K.E, and start moving slowly.
2. At certain temp, particles no longer energy to move, f.o.a become stronger, and pull particles together, so they settle into fixed positions.
3. Only vibrate in fixed positions, substance is now solid.
This certain temp at which a substance changes from liquid to solid is the freezing point.
Boiling
Substance's state changes from liquid to gas. How?1. Energy taken in, liquid particles gain K.E, start moving faster.
2. At certain temp, have enough energy to break through the f.o.a b/w liquid particles.
3. They break away, and start moving in rapid random directions. Substance is now gas.
This certain temp at which substance changes from liquid to gas is the boiling point.
You should know how to draw the cooling and heating curves. You can find them drawn in any of the chemistry books, or online too.
Heating curve:
A-B : heat is provided so that solid heats up. Temp of the substance increases till it reaches B.
B-C: At B, solid starts melting and changing into liquid. A mixture of liquid and solid exists here. This is the melting point!
(Remember that at this point the temp will not change, it will remain constant since the heat energy is being used up by the particles to overcome the f.o.a, so the graph here has to be a straight line).
C-D: At C, all the substance has melted and temp rises till it reaches D. Here substance is in liquid state.
D-E: At D, the temp is now enough for the liquid to start boiling. A mixture of liquid and gas exists here. This is the boiling point! (Over here too, temp remains constant, since energy is used up by particles to change state) > graph is again a straight line.
E-F: At this point, substance is in gaseous state.
Note: In the exam, either they can give you both the melting and boiling points and ask you to plot a graph and tell what’s happening at each stage or they can also ask you to draw just a part of it. It depends on the question.
Cooling curve:A-B: Temp is dropped so that the gas/vapours condense. Temp of the substance decreases till it reaches B.
B-C: At B, vapours start condensing and changing into liquid. A mixture of liquid and gas exists here. (Remember that at this point the temp will not change, it will remain constant since the heat energy is released to the surroundings by the particles to gain f.o.a, so the graph here has to be a straight line).
C-D: At C, all the substance has condensed and temp drops till it reaches D. Here substance is in liquid state.
D-E: At D, the temp is now dropped enough for the liquid to start freezing. A mixture of liquid and solid exists here. This is the freezing point! (Over here too, temp remains constant, since energy is released by particles to change state) > Graph is again a straight line.
E-F: At this point, substance is in solid state, since all the liquid has now frozen.
Remember: The heating curve starts from the bottom of the graph, because heat increases.
But a cooling curve starts from the top, because heat decreases. Don’t make them the other way round or they will be completely wrong!
Now, just a little bit about evaporation...
What’s evaporation? When liquids turn into a gas at temps lower than the boiling point.
You should know about volatile liquids.
What are they? They are liquids that evaporate very quickly at room temp. And they normally have boiling points above room temp.
Examples of volatile substances?
Petrol, perfumes, nail polish remover etc. If you leave them open, they'll evaporate in no time.
They can ask you the difference between evaporation and boiling. Evaporation and boiling both involve changing liquid into gas. > Similarity.
However,
1. boiling occurs only at boiling point, but evaporation occurs below boiling point.
2. boiling occurs throughout the liquid, but evaporation only occurs at the surface of the liquid.
3. Boiling occurs rapidly, and you can see bubbles forming, but evaporation occurs slowly, and you may not see bubbles.
Now if they ask you that compare and contrast between evaporation and boiling, then you have to write down the similarity and all the three differences. If you don’t write the similarity you will lose marks.
And if the question is only about differences, then only talk about the differences.
Then there is condensation. What’s that? When a gas is cooled, it turns into a liquid, means it has condensed.
Remember that it occurs when vapours touch a cold surface.
Now whats the chemistry behind condensation? (it’s sort of a reverse of boiling)1. heat energy is lost, temp drops, particles lose kinetic energy, and start moving slowly.
2. by time, the movement becomes too slow, gain in f.o.a, gas turns liquid.
Sublimation comes next. What’s that? When solids change directly into a gas without going to the liquid phase, or from a gas to a solid, it’s called sublimation.
How?
When particles gain enough energy to break away from solid into gas. so much gain in K.E, that they break away. and f.o.a are completely broken.
similarly, when gas particles are lose energy to such a degree that they have hardly any K.E, and f.o.a are very strong, a solid is made.
Uses of sublimation1. dry ice sublimes, its used for industrial refrigeration and transporting frozen goods.
why? its useful because it keeps frozen food very cold and when they are taken out, it evaporates, leaving no liquid behind.
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