The Particular Nature of Matter | State of Matter | Inter Conversion of States of Matter | Heating and Cooling Curves | Kinetic Theory | Structure of Particles | 3 States of Matter | Diffusion

1.0 Lesson Objectives

• States of Matter
• Inter-conversion of States of Matter
• Heating and Cooling Curves
• Kinetic Theory
• Structure of Particles in 3 States of Matter
• Diffusion Kinetic Theory
• Porous Pot
• Tube Experiment
• Gas Jar Experiment

1.1 States of Matter:

Matter:

Any substance that occupies some space and has some mass is called Matter.

States of Matter:

States of Matter mean the forms in which matter exists in our environment. There are three states of Matter:

• Solids
• Liquids
• Gases

Properties of States of Matter:

The table below tells us about some of the important properties of the three states of matter.

• Two important points to note here:
  • The compressibility is inversely proportional to density of a substance: more dense substances are harder to compress
  • The ease of flow is directly proportional to kinetic Energy: more kinetic energy means the substance will flow easily. Kinetic Energy is discussed further ahead.

1.2 Interconversion of States of Matter:

There are 6 conversions that are possible between the three states of matter as illustrated in the diagram. We shall go through each of them.   In the diagram above, it can be noted that the orange cycle represents processes that release heat and the blue cycle represents processes that absorb heat. This will be further elaborated in Kinetic Theory.

Evaporation:

Evaporation is the process by which a liquid turn into a gas (at any temperature lower than boiling point).

Condensation:

Condensation is the process in which a gas releases heat and turns into a liquid.

Melting:

Melting is the process by which a solid turn into a liquid by absorbing heat.

Freezing:

The change in the state of matter where a liquid turn into a solid is known as freezing.

Solidification:

The change in the state of matter from gas to solid without a liquid phase in between is called solidification.

Sublimation:

The process in which a solid turn directly into a gas with no liquid phase in between is called sublimation.

Melting and Boiling Point:

• Melting Point: The constant temperature at which a pure solid turn into a liquid is called the melting point of that solid. It is the same temperature at which that pure liquid can turn into a solid. (also the freezing point)
• Boiling Point: The constant temperature at which a pure liquid turn into a gas is called the boiling point of that liquid. (also the condensation point)

Effect of Impurities on melting and boiling points:

• If we want to test whether a substance is pure or not, we can use its melting and boiling points. Pure substances have fixed MP and BP.
• Impurities will:
  • Increase boiling point of liquids
  • Decrease melting point of liquids.

Predicting the State using Melting and Boiling Points:

• Both boiling point and melting point above room temperature: Solid, as this mean we will need to provide more heat than already present in the room to melt the solid.
• Boiling point above room temperature and melting point below room temperature: Liquid, as there is enough heat in the room to change from solid to liquid but not enough to turn the substance into a gas.
• Both boiling and melting point below room temperature: Gas, there is enough heat in the room for the gas state to exist.
• If melting point is lower than room temperature but boiling point is slightly higher, then the state is Volatile Liquid (liquids that quickly turn to gas e.g. alcohol)

1.3 Heating and Cooling Curves:

Heating and cooling curves are used to understand the changes in states of matter for a substance. They can tell the melting and boiling point of a substance and the time it takes to change states.

Heating Curve:

As the name suggests, the heating curve shows a substance that is provided heat over a period of time. We start off with a solid and keep providing heat until we are left with a gas and the process is clocked over fixed intervals such as minutes.

• The picture shows the heating curve for a block of ice.
• We start at a temperature below 0 degrees which is our melting point of ice.
• In this temperature, our ice is in solid state.
• As we keep providing heat from A-B, the solid state of ice is maintained since the temperature is below melting point.
• When we reach B, the melting point, the ice starts to change state from solid to a liquid ( B-C) and the temperature becomes steady. This is because all the heat that is being provided is absorbed by the ice to change its state. This horizontal segment indicates the change of state in the curve.
• After C, until we reach the boiling point, the heat provided is not enough to completely change the state from liquid to a gas. Evaporation occurs during this time, but our state is still liquid.
• From C-D, again there is enough heat for the liquid to boil and turn into a gas and so the temperature becomes steady again. This is because the heat that is being provided is taken in by the liquid to change its state. After all the liquid turns into a gas, the temperature starts rising again from E-F where our substance exists in vapor state.

Cooling Curve:

The cooling curve shows a substance that is cold down over a period of time. We start off with a gas and keep cooling it down until we are left with a solid and the process is clocked over fixed intervals such as minutes. This is the inverse form of heating curve.

• The picture shows the cooling curve for water vapors.
• We start at a temperature above 100 degrees which is our condensation point of water vapor.
• In this temperature, our water vapors are in a gaseous state.
• As we keep cooling down from A-B, the gaseous state of water vapor is maintained since the temperature is above condensation point.
• When we reach B, the boiling or condensation point, the vapors start to change state from gas to liquid (B-C) and the temperature becomes steady. This is because during the change of state, our gas release heat which doesn’t allow the temperature to go down. This horizontal segment indicates the change of state in the curve.
• After C, until we reach the melting point, the cooling is not enough to completely change the state from liquid to solid.
• From C-D, again we have reached the freezing point and our liquid starts to turn into a solid ice block and so the temperature becomes steady again. This is because the heat is given out in this change of state as well. After all the liquid turns into an ice, the temperature starts falling again from E-F where our substance exists in solid state.

Candle Burning Showing all three States:

One of the most commonly used examples to illustrate the three states of matter is a burning candle as shown below.

1.4 Diffusion:

Diffusion:

• Diffusion is the natural mixing of particles by the movement from a higher concentration to a lower concentration.
• In simpler words, when particles are clustered in an area, they have a higher concentration over there. Particles naturally move from that area and spread out evenly towards a lower concentration. This process is called diffusion.

Examples:

Some common examples of diffusion include:

• Perfume smell: when we spray perfume, the perfume particles are in a higher concentration and gradually they diffuse out towards the lower concentration.
• Food Aromas: the reason we are able to smell food being cooked from far away is that the particles diffuse from near the stove.
• Ink in water: If we place a drop of ink in water, slowly the entire glass will have a color of ink. This is because the ink has evenly diffused inside the glass from the higher concentration area where it was dropped.

Factors Effecting Diffusion:

• Mass: The rate of diffusion is inversely proportional to mass. If a gas is heavier, it will take more time to diffuse as compared to a lighter gas.
• Temperature: Temperature is directly proportional to diffusion rate. When there is more heat, diffusion takes place faster.
• Concentration Difference: Difference in concentration is inversely proportional to the time taken to complete the diffusion. When there is higher difference in concentration, diffusion rate is faster and hence, less time is needed for the diffusion to complete.
• State: Diffusion is faster in gases as gases are lighter and have more ease of flow.
• In order to diffuse, matter has to be made up of individual particles.

1.5 Kinetic Theory:

The kinetic theory states that matter is made up of particles and these particles are constantly in motion i.e. they have kinetic/movement energy. All state changes can be defined in terms of heat absorbing and releasing which ultimately is affecting the kinetic energy of particles.

Inter-conversion of States – Kinetic Theory:

Solid -> Liquid -> Gas:

• When a solid is heated till its melting point, it absorbs heat energy. The particles of solids start to move faster and gain kinetic energy and hence they become further apart and turn into a liquid.
• When the liquid is heated up till the boiling point, the particles of the liquid gain even more heat energy and they start to escape the surface of the liquid and turn into a gas.
• While the state is being changed, there is no change in temperature, as discussed earlier, because the particles are taking up the heat provided to increase their movement.

Gas -> Liquid -> Solid:

• On the other hand, if we cool a gas down, it will release its heat to the surrounding and hence, its particles will come closer together and decrease in movement. This will turn a gas into a liquid.
• When the liquid is further cooled down, its particles lose all the excess kinetic energy and become tightly packed, with only a vibrating motion left, and form solid state. They release this energy to the surrounding.
• The temperature does not lower when a state change is taking place as more and more heat is being released to the surrounding.

1.6 Structure of Particles in 3 States of Matter:

As shown in the above diagrams of state change, there are structural differences in the particle arrangement of the three states of matter.

Solids:

• Very close together,
• Arranged in a regular form in rows,
• Held very tightly meaning stronger force of attraction,
• Not moving from their position, just vibrating

Liquids:

• Further apart as compared to solids,
• Not regularly arranged,
• Not tightly held so weak attraction,
• Moving about and changing places

Gases:

• Furthest apart among the three states,
• Randomly arranged,
• Free to move completely,
• Moving very fast in all directions, and possessing a high kinetic energy

1.7 Diffusion Kinetic Theory:

Diffusion Kinetic theory states that diffusion is due to the kinetic energy that is possessed by matter. Whenever there is an area of higher concentration, particles move from that area towards the lower concentration idea since the particles are moving in all directions in random motion.

Temperatures effect on Diffusion:

• In accordance to the kinetic theory, when temperature is increased, the particles gain more energy and they start to move around faster. This allows faster movement from higher to lower concentration and ultimately, faster diffusion.
• On the other hand, when the temperature is decreased, the energy possessed by particles is released to the surrounding and they move slowly, taking more time to diffuse out and become easily distributed in the surrounding.

Temperature effect on the pressure of a Gas:

• When temperature is increased keeping the volume constant, the pressure increases and vice versa. This is due to the fact that with an increase in temperature, the particles move fast and collide with the walls of the container more often, resulting in a higher pressure.
• This can be explained with the example of a balloon. If we heat a filled balloon, the particles of air inside the balloon gain heat energy and start to move faster. They collide with the balloon walls more often and hence, to cancel this change, the balloon size increases as the pressure outside the balloon is less than the pressure from inside the balloon.
• On the other hand, decreasing the temperature will result in slower movement of particles and less collisions with the wall of the balloon and so the internal pressure would be less as compared to the air pressure outside the balloon. This will cause the balloon to shrink in size.

1.8 Working of Porous Pot:

One of the most commonly used apparatus to demonstrate the effects of gas pressure is the porous pot. The apparatus setup is as follows.

• The porous pot is, as the name suggests, a porous container which allows gas to diffuse in and out of it.
• We begin by placing one gas ‘Z’ inside the porous pot and the other gas ‘W’ outside the porous pot.
• In the beginning, the level of mercury is steady on both sides as no diffusion has taken place. This is shown by a black level marking.
• There are three case scenarios of diffusion that are tested in a porous pot set up.
  • CASE 1: Both gases have an equal mass, there will be no change in the pressure inside the porous pot, and in the mercury level at X and Y as the gases will diffuse at the same rate.
  • CASE 2: If the gas ‘Z’ is heavier than the gas ‘W’, this means that the gas inside the porous pot will take longer to diffuse out and the gas outside the pot will diffuse in faster. This will result in more particles coming in than going out and ultimately, the pressure inside the pot will increase. This increase in pressure will cause the X level to go down and the Y level to rise up. (illustrated in the diagram below with red marks) As the diffusion continues to take place, the mercury level will come back to the original position since all the diffusion would be completed and gas particles outside and inside will be of the same concentration.

• • CASE 3: If gas ‘Z’ is lighter than the gas outside, ‘W’, then the lighter gas Z will diffuse out quicker than the diffusion inside of the gas W. This will result in the particles inside the porous pot to decrease, and hence the pressure inside will also decrease. In order to cater this change in Pressure, the level of mercury at X will rise up since the pressure on mercury from outside will be more as compared to the pressure from inside, and the level at Y will drop down, as illustrated below with red marks. After the process of diffusion ends, the level will return to the normal black marks again at X and Y.

1.9 Tube Experiment:

The tube experiment is another experiment that is used to depict diffusion. In this experiment, we use volatile liquids and soak cotton wool in two different types of liquids, setting the apparatus as shown below.

• As the time goes on, after a while, the liquids evaporate, and diffusion starts. We make sure the two substances used can react together when they meet.
• Both the vapors diffuse towards each other from high concentration to lower concentration and react to form a ring at the point of contact. The diffusion rate determines the position of the reaction and the formation of the ring.
• There are three cases to the ring formation:
  • CASE 1: Both the substances ‘K’ and ‘L’ have the same mass: In this case, the gases diffuse at the same rate and hence meet in the middle of the tube, an equal distance from both the cotton wool. This is where they form a ring as shown by position B in the Diagram below.

• CASE 2: The substance ‘K’ is heavier than substance ‘L’ and hence will diffuse slowly as compared to substance ‘L’. This means that Substance ‘L’ will diffuse a greater distance than substance ‘K’ in the same time resulting in the meeting point to be closer to K than to L. This is depicted by position A in the diagram below and the ring will form in this position in such a case.

• CASE 3: The substance ‘L’ is heavier than substance ‘K’ and hence will diffuse slowly as compared to substance ‘K’. This means that Substance ‘K’ will diffuse a greater distance than substance ‘L’ in the same time resulting in the meeting point to be closer to L than to K. This is depicted by position C in the diagram below and the ring will form in this position in such a case.

• The ring will always form near to the heavier gas.
• The evaporation and diffusion take a while before the ring starts to appear.
• The more the difference in mass, the more distance will be there between the center of the tube and the ring.

2.0 Gas Jar Experiment:

• In this experiment, we place a dark colored gas such as bromine in a gas jar and fill the other jar with air. Then we set up the apparatus as follows, remove the lids, and leave it for a few days.
• What is noted is that the concentration of bromine will be higher in the jar below and so the particles will diffuse from the higher concentrated jar to the lower concentrated jar at the top. Similarly, air will diffuse from the jar above to the jar below.
• The changes that would be noted due to diffusion will be an equal diffusion in both jars after several days and a lighter color of bromine since air is also equally diffused in the jars. This simple experiment demonstrates diffusion.

Lesson Tags

Particular Nature of Matter | States of Matter | Heating and Cooling Curves | Detailed Notes For Preparation & Revision | O Level Chemistry 5070 and IGCSE Chemistry 0620

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