IGCSE Chemistry 0620 Past Paper - MIS 2024-2025 - PDF

MIS 2024-2025 Secondary School Department IGCSE – Chemistry 0620 By: Dr. Mahjoub Afandi Chapter – 1: STATES OF MATTER  LEARNING OBJECTIVES 1 STATES OF MATTER 1.1 Solids, liquids and gases 1. State the distinguishi...

MIS 2024-2025 Secondary School Department IGCSE – Chemistry 0620 By: Dr. Mahjoub Afandi Chapter – 1: STATES OF MATTER  LEARNING OBJECTIVES 1 STATES OF MATTER 1.1 Solids, liquids and gases 1. State the distinguishing properties of solids, liquids and gases. 2. Describe the structures of solids, 1.2 Diffusion liquids and gases in terms of particle separation, arrangement and motion. 1. Describe and explain diffusion in 3. Describe changes of state in terms of terms of kinetic particle theory. melting, boiling, evaporating, freezing and 2. Describe and explain the effect condensing. of relative molecular mass on the 4. Describe the effects of temperature rate of diffusion of gases. and pressure on the volume of a gas. 5. Explain changes of state in terms of kinetic particle theory, including the interpretation of heating and cooling curves. 6. Explain, in terms of kinetic particle theory, the effects of temperature and pressure on the volume of a gas. Everything is Made of Particles Particles: the big idea in chemistry. All chemistry is based on one big idea: that everything is made of very tiny pieces called particles. The evidence around you: Most particles are so small that we cannot see them directly, even with the most powerful microscope. But there is evidence for them all around you. Outside the lab: 1 In sunlit rooms, you sometimes 2 Cooking smells spread. The see dust dancing in the air. ‘smells’ are due to particles which It dances because the dust specks spread because they are are being bombarded by tiny bombarded by the particles in air. particles in the air, too small to This is an example of diffusion. see. Just like those pollen (See pages 3 and 11.) Some end granules in water. up in your nose!  In the Lab: 3 Place a crystal of purple potassium 4 Place an open gas jar of air upside down on manganate (VII) in a beaker of water. The an open gas jar containing a few drops of colour spreads through the water, because red-brown bromine. The colour spreads particles leave the solid crystal- it dissolves upwards because the particles of bromine - and spread among the water particles. vapour mix among the gas particles in the air. Diffusion: The particles mix and spread by colliding with other particles, and bouncing off in all directions. This mixing process is called diffusion. It takes place in liquids and gases. The result is that particles spread from where they are more concentrated, until all the particles are evenly mixed. So what are these tiny particles? The smallest particles, that we cannot break down further in chemical reactions, are called atoms. In some substances, the particles are just single atoms. For example, air contains single atoms of argon. In many substances, the particles consist of two or more atoms joined together. These particles are called molecules. Water and bromine exist as molecules. Air is mostly nitrogen and oxygen molecules. In other substances the particles are atoms or groups of atoms that carry a charge. These particles are called ions. States of Matter  States of Matter What’s the difference? Solids Liquids Gases Shape Fixed Shape of the Shape of the container container Volume Fixed Fixed volume of the container Movement Only Flows easily Move freely vibration Arrangement Regular Random Random (lattice) Separation Touching Touching Not touching Changes of State Gas Liquid Solid  Changes of State Gas Liquid melting { Solid  Changes of State Gas Boiling (evaporating) { Liquid melting { Solid  Changes of State Gas Boiling (evaporating) { Liquid } condensing melting { Solid  Changes of State Gas Boiling (evaporating) { Liquid } condensing melting { } freezing Solid  Changes of State Solid Gas  Changes of State sublimation { Solid Gas  Changes of State Solid Gas {deposition  Changes of State Gas Liquid Particles are fixed in place and cannot move Solid (only vibration)  Changes of State Gas Particles are free to move within a Liquid container (free surface) Particles are fixed in place and cannot move Solid (only vibration)  Changes of State Particles are free to move about (move Gas freely in all directions) Particles are free to move within a Liquid container (free surface) Particles are fixed in place and cannot move Solid (only vibration) The particles in Solids, Liquids, and Gases  SOLIDS Strong forces of attraction held in fixed position lattice arrangement don’t move, so have definite shape and volume vibrate  SOLIDS as they become hotter, the particles vibrate more. so they expand can’t be compressed generally very dense  SOLIDS when heated, molecules gain energy. they vibrate more and more strong forces are overcome, molecules start to move = MELTED  SOLIDS so; The particles in a solid are arranged in a regular pattern or lattice. Strong forces hold them together. They cannot leave their positions. The only movements they make are tiny vibrations.  LIQUIDS Some attraction between molecules. free to move within the container no definite shape, but take shape of container random arrangement  LIQUIDS when heated, they move faster and expand can’t be compressed quite dense  LIQUIDS heat makes the molecules move faster as they gain energy. fast moving molecules at the surface will overcome forces of attraction and escape = EVAPORATION  LIQUIDS So; The particles in a liquid can move about and slide past each other. They are still close together, but not in a lattice. The forces that hold them together are weaker than in a solid.  GASES no force of attraction free to move in all directions, travel in straight lines sometimes collide no definite shape or volume, expand to fill space  GASES exert pressure on wall of container arranged randomly move faster when heated can be compressed very low densities  GASES So; The particles in a gas are far apart, and they move about very quickly. There are almost no forces holding them together. They collide with each other and bounce off in all directions.  Changes of State Melting When a solid is heated, its particles get more energy and vibrate more. This makes the solid expand. At the melting point, the particles vibrate so much that they break away from their positions. The solid turns liquid. Boiling When a liquid is heated, its particles get more energy and move faster. They collide more often, and bounce further apart. This makes the liquid expand. At the boiling point, the particles get enough energy to overcome the forces between them. They break away to form a gas. Evaporating Even well below the boiling point, some particles in a liquid have enough energy to escape and form a gas. Evaporation takes place at the surface of the liquid, and over a range of temperatures. It is a slower process than boiling. (Boiling takes place throughout the liquid, and at a specific temperature.)  Changes of State How much heat is needed? The amount of heat needed to melt or boil a substance is different for every substance. That’s because the particles in each substance are different, with different forces of attraction between them. The stronger the forces, the more heat energy is needed to overcome them. So the higher the melting and boiling points will be. The kinetic particle theory A substance can be a solid, a liquid, or a gas, and change from one state to another. It has different characteristics in each state. (For example, solids do not flow.) The differences are due to the way its particles are arranged, and move, in each state. Together, these ideas make up the kinetic particle theory. (Kinetic means about motion.) Heating and Cooling Curves  Heating Curve This graph is called a heating curve. A heating curve shows how the temperature of a substance changes as you heat it up. Temperatures remain constant while water changes state. These temperatures are its melting Temperature and boiling points. Gas Boiling point Liquid Melting point Solid Time Explaining Heating Curve  Cooling Curve A cooling curve shows how the temperature of a substance changes as you cool it down. As you can see, this curve is the mirror image of the Gas Temperature heating curve. The temperature remains constant as the substance changes state. Condensing Liquid Freezing Solid Time Explaining Cooling Curve Not just water... You can draw heating and cooling curves for any substance. They are different for each substance. That’s because they depend on the particles and the forces between them. The heating curve on the right is for iron. What if a substance is not pure? The graphs here are for pure water and iron. A pure substance has only one type of particle. And it has sharp melting and boiling points, which you can find from the heating curve. But if other types of particle are mixed in, they affect the forces between particles. Changes of state will now occur over a range of temperatures, not sharply. So lines like BC and DE on this graph will be tilted, not Hat. This means that melting and boiling points can be used to check whether a substance is pure. A Closer Look at Gases Gases and Pressure What is gas pressure? When you blow up a balloon, you fill it with air particles. As they move about, they collide with the sides of the balloon, and exert pressure on it. This pressure keeps the balloon inflated. In the same way, all gases exert pressure on the walls of their containers. When you change the temperature of a gas: Look at the container of gas below. The piston can move freely up or down, until the pressure is the same inside and outside the container.  Gases and Pressure When you change the pressure of a gas: The same is true for all gases, at constant temperature: An increase in pressure means a decrease in volume, for a gas. A decrease in pressure means an increase in volume, for a gas. In fact, if you increase the pressure on a gas enough, you can push its particles so close together that a gas turns into a liquid.  Diffusion The particles mix and spread by colliding with other particles, and bouncing off in all directions. This mixing process is called diffusion. It takes place in liquids and gases. The result is that particles spread from where they are more concentrated, until all the particles are evenly mixed. The rate of diffusion of gases An experiment to compare rates of diffusion: The particles in hydrogen chloride gas are twice as heavy as those in ammonia gas. So which gas do you think will diffuse faster? Let’s see: Cotton wool soaked in ammonia solution is put into one end of a long tube (at A below). It gives off ammonia gas. At the same time, cotton wool soaked in hydrochloric acid is put into the other end of the tube (at B). It gives off valid hydrogen chloride gas. Gases diffuse along the tube. White smoke forms where they meet: The white smoke forms closer to B. So the ammonia particles have travelled further than the hydrogen chloride particles- which means they have travelled faster. The rate of diffusion The lower the mass of its particles, the faster a gas will diffuse. This makes sense when you think about it. When particles collide and bounce away, the lighter particles will bounce further and faster. The particles in the two gases above are molecules. The mass of a molecule is called its relative molecular mass. So we can also say: The lower its relative molecular mass, the faster a gas will diffuse. Note that everything in the experiment above needs to be at the same temperature (room temperature) for a valid test. That is because, as you know, the temperature also affects how fast gas particles move. An increase in temperature means an increase in rate of diffusion. End of Chapter One