CHE 5124 MATTER

Welcome to today's lesson. We are looking at chemistry which is science paper 2 according to the ECZ curriculum. So the topic we are dealing with today is matter and changes of state of matter. So today's topic has been specially designed and summarized for you so that you are equipped to answer any question in the exam to do with matter and its changes of state. So please pay attention, this will benefit you. Okay, so matter is simply anything that occupies space and has some mass. So matter has got three basic units. So the three basic units of matter is simply the atoms, ions and molecules. Again, matter has got three states. It's found in three states. So it can be found in the solid state, it can also be found in the liquid state, it can also be found in the gaseous state. So an example of a solid is a stone, an example of a liquid is water, an example of a gas is the oxygen that we breathe. Okay, now matter has been known to be composed of tiny particles that are in constant random motion and we have two experimental based evidences that will support this theory which is the diffusion and that of Brownian motion. Okay, now let's try to look at the characteristics and the changes of state of matter. So this diagram here is illustrating a lot, so please pay attention as I bring out the characteristics and also the changes of state and their importance. So on the first state here, this one here represents a solid state. Okay, so in the solid state, the particles are closely packed together and arranged in a regular pattern. Okay, so the solids, they have a fixed shape and a fixed volume. Okay, so because their particles are closely packed together, the solids cannot actually be compressed. Okay, then these particles, they vibrate about their fixed positions. Okay, so now what happens is if you keep on applying heat, we are heating a solid. When you keep applying heat, these particles in here are going to absorb enough kinetic energy. When they absorb enough kinetic energy, they will begin to increase. The particle distance will begin to increase as they vibrate about. So as the particle distance slightly increases, then the solid will assume a new state of matter which is the liquid state. So as you can see, in the liquid state, the particles are still closely packed together but not as packed as a solid. Okay, so in here, we are going to say that the particles also here, they vibrate and move at short distances. So they vibrate and move at short distances. So making solids to have a fixed volume but no fixed shape. So liquid, we are saying they have a fixed volume but no fixed shape. So they take up the shape of a container. So again here, we are saying because this particles are not, they are not so much spaced, the liquid can also not be compressed. So those are some of the characteristics. So as we continue applying the heat to the liquid here, you discover that these particles, they will gain more and more kinetic energy leading to an increase in their particle distance. So particle distance is simply the distance between the particles in a state of matter. Okay, so as the distance increases, then this one is going to now assume a new state which is the gaseous state. Okay, so talking about the gaseous state, as you can see, the particles are further apart. So because the particles are further apart, the gases have got no fixed volume and no fixed shape. Okay, so no fixed shape, no fixed volume. The particles in here, they are able to move randomly. Okay, so this means that gases can easily be compressed. Okay, so that's what happens when you are adding heat. So now, the change, as you are adding heat from a solid to a liquid, the change of state from solid to liquid is what we call melting. And melting has got a lot of uses in real life. So melting can be used to cut metals in industries. Okay, then the change of state from liquid to gas, this one is called evaporation, though some people confuse it to boiling as well, but that will be discussed. So from liquid to gas is known as evaporation. So evaporation has got uses in life. For example, it is used in drying clothes. So when we hang our wet clothes on the line, evaporation will take place and the clothes will remain wet, dry. Okay, it is also used in obtaining crystals, informing crystals, so separating crystals from a solution. Okay, so now this is going forward. So the reverse is also true. A situation now where you are removing heat. Okay, so when you begin to remove the heat, the opposite is going to happen. So when you remove heat from a gas here, there is another change of state that is going to take place, which we call condensation. So it will condense back to a liquid. Then again, when you keep on removing the heat, for example, if you put a gas in the fridge, you keep removing the heat, this liquid can also be frozen back to a solid, like water turning to ice. So meaning the change of state from liquid to solid is what we call freezing or solidification. Okay, now there are also certain unique circumstances where you can change when you heat a solid rapidly, it is going to change directly from a solid to a gas. And that one is what we call sublimation. So examples of substances that can sublime is ammonium sulfate, or iodine crystals. Okay, those can actually sublime, even carbon dioxide also undergoes sublimation. Then also, just like this one is, there's an opposite, you can also rapidly cool a gas, which will turn directly to a solid without first going into the liquid state. So that rapid change there is what is called deposition. Okay, so this is summarizes the characteristics and changes of state of matter, the three states of matter. So now, like I mentioned, the change of state from a liquid to a gas, people call it evaporation, which is the correct thing. So some, they actually confuse it to boiling. So let's just look at a few differences between boiling and evaporation. So now, both processes, boiling and evaporation, they involve application of heat. But the difference is that boiling occurs throughout the liquid, whereas evaporation takes place at the surface of the liquid. Okay, then also when you are boiling, you notice there's a lot of bubbles that have been produced, whereas evaporation occurs slowly without any bubbles, you can't see anything. Okay, then boiling most importantly, it occurs at a specific temperature, which we call the boiling point. For example, water has got a boiling point of 100 degrees Celsius. But when you look at evaporation, it occurs at any temperature. Okay, so this is a summary of the processes that take place when matter is changing from one state to another. And the changes of state of matter is based on the application and removal of heat. Okay, so with this summary that has been given, I believe you can answer any, I repeat, any exam question that can come under this topic. So for practice purposes, you are going to check Science Paper 2, 2016 for the internals, Section B, Question 1, answer that question. Then Science Paper 2, 2018 for the internals as well, Section B, Question B1, answer that one. And lastly, but not the least, check Science Paper 2, 2019 for the internals, Section B, answer Question B1 and Question B2A. You can answer those with this knowledge that you have been given. Thank you so much for your attention. Till next time.