IGCSE Chemistry - Topic 1 - States of Matter PDF

IGCSE Chemistry – Topic 1 Mrs. Larisa Thomas STATES OF MATTER PROPERTIES OF SOLIDS, LIQUIDS GASES  SOLIDS Solids have a fixed volume and shape They have a high density The atoms vibrate in position but can’t change location The partic...

IGCSE Chemistry – Topic 1 Mrs. Larisa Thomas STATES OF MATTER PROPERTIES OF SOLIDS, LIQUIDS GASES  SOLIDS Solids have a fixed volume and shape They have a high density The atoms vibrate in position but can’t change location The particles are packed very closely together in a fixed and regular pattern This regular pattern is called a lattice  LIQUIDS Liquids have a fixed volume but adopt the shape of the container They are generally less dense than solids (except water) but much denser than gases The particles move and slide past each other This is why liquids adopt the shape of the container and why they can flow freely  GASES Gases don’t have a fixed volume and take up the shape of the container They have very low density There is a lot of space between the particles so gases can be compressed into a smaller volume Particles are far apart and move randomly and quickly in all directions They collide with each other and the sides of a container This is how pressure is created inside a can of gas State Solid Liquid Gas Particle Particles close together: Particles close together: Particles far apart Separation tightly packed loosely packed Arrangement of Regular pattern - lattice Randomly arranged Randomly arranged Particles Motion of Vibrate around a fixed Move or slide around each Move quickly in all directions Particles position other (straight lines) Energy of Low kinetic energy Medium kinetic energy High kinetic energy Particles Density High Medium Low Not fixed – Fluid shape Not fixed – Fluid shape Shape Fixed shape Takes shape of container Takes shape of container Not fixed – expands to fill Volume Fixed volume Fixed volume container 2D Diagram SOLID LIQUID GAS CHANGES OF STATE  MELTING Melting is when a solid changes into a liquid Requires an increase in temperature by supplying heat energy which is transformed into kinetic energy, allowing the particles to vibrate more vigorously Occurs at a specific temperature known as the melting point (m.p.) FREEZING Freezing is when a liquid changes into a solid This is the reverse of melting and occurs at the same temperature The melting and freezing point of a pure substance is the same Requires a significant decrease in temperature (loss of heat energy) and occurs at a specific temperature known as the freezing point  EVAPORATING When a liquid changes into a gas over a range of temperatures Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquid's surface at low temperatures (below the b.p.) The larger the surface area and the warmer the surface of the liquid, the quicker a liquid can evaporate BOILING Boiling is when a liquid changes into a gas Heating causes bubbles of gas to form below the surface of a liquid (liquid particles escape from the surface and within the liquid) Occurs at a specific temperature known as the boiling point (b.p.)  CONDENSING When a gas changes into a liquid on cooling and it takes place over a range of temperatures When a gas is cooled its particles lose energy and when they bump into each other they lack the energy to bounce away again, instead they group together to form a liquid Changes of State  What is the state? With information about the melting and boiling points of a substance, one can identify the state the substance is in at a specific temperature If the given temperature is below the melting point (freezing point) → the substance will be a solid at that temperature If the given temperature is between the melting point and boiling point→ the substance will be a liquid at that temperature If the given temperature is above the boiling point→ the substance will be a gas at that temperature  Melting Boiling point point SOLID LIQUID GAS Between melting and Below melting point boiling point Above boiling point  The Kinetic Particle Theory The Kinetic Particle Theory states the following All matter is made up of very small particles The particles are in constant random motion → They have kinetic energy There are spaces between the particles → Intermolecular spaces There are attractive forces between the particles → Intermolecular forces  State Changes - Kinetic Theory MELTING → A solid is heated and the heat energy supplied is transformed into kinetic energy. Increased kinetic energy causes stronger vibrations until the particles have enough energy to weaken the intermolecular forces holding them in a regular arrangement. The intermolecular spaces will increase as particles break away from the lattice arrangement to form a liquid. FREEZING → As a liquid is cooled down, the kinetic energy of the particles decrease, and they start moving slower. At a certain temperature, their motion becomes slow enough for the forces of attraction to be able to hold the particles together in a regular arrangement of a solid. As the intermolecular forces become stronger, the intermolecular spaces become smaller. BOILING → A liquid is heated, and the heat energy supplied is transformed into kinetic energy. An increase in kinetic energy causes the particles to move faster and further until the particles move fast enough to overcome (break all) the intermolecular forces holding them together. The intermolecular spaces will increase as particles break away from the liquid arrangement to form a gas. CONDENSING → As a gas is cooled, the kinetic energy of the particles decrease, and they start moving slower. At a certain temperature, the gas particles will slow down enough for the attractive forces to become strong enough to hold them together in a liquid arrangement. As the intermolecular forces become stronger, the intermolecular spaces become smaller.  State Changes & Kinetic Theory - Summary When substances are heated, the particles absorb heat (thermal) energy which is converted into kinetic energy An increase in kinetic energy in a solid causes the particles to vibrate more and as the temperature increases, they vibrate so much that the solid expands until the structure breaks and the solid melts On further heating, the particles in the now liquid substance also absorbs heat energy, which is converted into kinetic energy, causing the particles to move more and faster The liquid expands more and some particles at the surface gain enough energy to overcome the intermolecular forces and evaporate When the boiling point temperature is reached, all the particles gain enough energy to escape, and the liquids boils  HEATING AND COOLING CURVES  State Changes on Graphs Changes in state can be shown on graphs called heating curves and cooling curves. These curves show how changes in temperature affect changes of state.  A heating curve shows the change of state of a Heating Curve substance from solid to gas when it is heated  Interpreting a Heating Curve Heating a solid results in its temperature rising over the time of heating but the graph shows two periods during which the temperature remains constant The temperature is constant during the phase changes → melting and vaporisation In the regions where the temperature rises: The heat energy added is transformed into kinetic energy so temperature increases Increased kinetic energy causes the particles to move faster and interact less strongly The intermolecular spaces increase as the particles begin to move apart In the regions where the temperature is constant: The heat energy added is used to overcome the intermolecular forces The heat energy causes changes in potential energy NOT kinetic energy This results in the temperature staying constant until the phase change is complete  Plateau = Phase change = Potential energy change  A cooling curve shows the change of state of a Cooling Curve substance from gas to solid when it is cooled  Interpreting a Cooling Curve Cooling a gas results in its temperature falling over the time of cooling The temperature is constant during the two phase changes → condensing and freezing In the regions where the temperature falls: Kinetic energy is transformed into heat energy that is removed so temperature decreases Decreased kinetic energy causes the particles to move slower and interact stronger The intermolecular spaces decrease as the particles begin to move closer together In the regions where the temperature is constant: The heat energy removed comes from energy released when forming new intermolecular forces The heat energy comes from changes in potential energy NOT kinetic energy The temperature stays constant until the phase change is complete  Pure VS Impure Substances Pure Substance → A substance that consists of only one type of element or compound Impure Substance → A substance that consists of more than one type of element and/or compound not chemically bonded Mixtures (pure substances physically mixed with impurities) are impure substances Impurities causes the melting point of an impure substance to be lower than the pure substance and causes it to melt over a range of temperatures Impurities causes the boiling point of an impure substance to be higher than the pure substance and causes it to boil over a range of temperatures Pure substances have specific and fixed melting and boiling points Phase changes on a heating or cooling curve are horizontal/flat lines Impure substances melt and boil over a range of temperatures Phase changes on a heating or cooling curve are slope lines with a gradient Pure Substances Heating Curve A pure substance boils at a specific and constant temperature A pure substance melts at a specific and constant temperature Impure Substances Heating Curve An impure substance boils at a higher temperature and over a range of temperatures An impure substance melts at a lower temperature and over a range of temperatures VOLUME OF GASES  Effect of Temperature & Pressure on the VOLUME of a Gas Inversely Changing the external pressure on a sample of gas Proportional An increase in pressure produces a decrease in volume → Gas is compressed A decrease in pressure produces an increase in volume → Gas expands Directly Changing the temperature of a sample of gas Proportional An increase in temperature produces an increase in volume → Gas expands A decrease in temperature produces a decrease in volume → Gas is compressed The large intermolecular spaces in gases explain why the volume is easily changed by changes in temperature and pressure Effect of Temperature on the Volume of a Gas Kinetic Theory Increase in temperature → The kinetic energy of the gas particles increase; they move faster and there is less chance of interaction between them as the intermolecular forces become almost negligent. They can move further apart to occupy a greater volume. Decrease in temperature → The kinetic energy of the gas particles decrease; they move slower, and they are more likely to interact with each other as the intermolecular forces have a greater effect. They will move closer together to occupy a smaller volume.  Effect of Pressure on the Volume of a Gas Kinetic Theory Increase in pressure→ The gas particles are pushed closer together and are more likely to interact with each other as the intermolecular forces have a greater effect. They will move closer together to occupy a smaller space/volume. Decrease in pressure→ The gas particles are not pushed together and are less likely to interact with each other as the intermolecular forces will have less of an effect. They will move further apart and occupy a greater space/volume.  Gas Pressure Gas particles are in constant and random motion The pressure that a gas creates inside a closed container is produced by the gas particles hitting the inside walls of the container  Effect of Temperature and Volume on Gas Pressure IINCREASE in TEMPERATURE → The heat energy supplied is transformed into kinetic energy. This increases the kinetic energy of the gas particles, so they move faster and collide with the walls of the container more frequently. The pressure will increase. DECREASE in VOLUME → If the container is made smaller, the same amount of gas particles will have less space available to move in and will collide with the walls of the container more frequently. The pressure will increase. Decreasing the volume of a container increases the gas pressure DIFFUSION  Diffusion The movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient, until equilibrium is reached Equilibrium means that eventually the concentration of particles will be equal as they spread out evenly to occupy all the available space This is the process by which different gases or liquids mix and is due to the random motion of their particles Diffusion can only happen in fluids (liquids and gases) because they have large enough intermolecular spaces for the particles to move around and spread out Diffusion cannot happen in solids because the intermolecular spaces are very small and the particles only vibrate, they do not move around to spread out evenly Diffusion of potassium manganate(VII), KMnO4 , in water. After a few hours, the concentration of KMnO4 is the same throughout the solution  Diffusion Rate & Molecular Mass Diffusion occurs much faster in gases than in liquids as gaseous particles move much quicker than liquid particles At the same temperature, different gases do not diffuse at the same rate This is due to the difference in their relative molecular masses Particles with a lower relative molecular mass is lighter, can move faster and further and therefore will diffuse at a faster rate Particles with a higher relative molecular mass is heavier, they move slower and therefore will diffuse at a slower rate  This can be demonstrated in the reaction between ammonia (NH3) and hydrogen chloride gas (HCl) inside a long glass tube Where the two gases meet, a white smoke of ammonium chloride (NH4Cl) forms This does not occur in the middle of the tube, but much closer to the end with the hydrogen chloride Hydrogen chloride has a relative molecular mass of 36.5 and ammonia of 17 The ammonia molecules are lighter, move faster and thus diffuse faster  Diffusion Rate & Temperature Diffusion is a passive process, which means that it happens on its own and no energy input is required Particles of the same substance has the same molecular mass but will diffuse at different rates if the temperature differs For the same substance, the rate of diffusion is faster at a higher temperature as the particles will have more kinetic energy and move faster For the same substance, the rate of diffusion is slower at a lower temperature as the particles will have less kinetic energy and move slower Topic Summary