Cambridge CIE IGCSE Physics Kinetic Particle Model of Matter PDF

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Physics Your notes Kinetic Particle Model of Matter Contents States of Matter Molecular Matter Particle Model of Gases Brownian Motion Gase...

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Physics Your notes Kinetic Particle Model of Matter Contents States of Matter Molecular Matter Particle Model of Gases Brownian Motion Gases & Absolute Temperature Page 1 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources States of Matter Your notes Properties of solids, liquids & gases The three states of matter The three states of matter in terms of shape and volume Solids Solids have a definite shape and a definite volume Solids cannot flow and are not compressible Liquids Liquids have no definite shape but do have a definite volume Liquids are able to flow to take the shape of a container but they are not compressible Gases Gases have no definite shape and no fixed volume Gases can flow to take the shape of their container and are highly compressible Page 2 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Changes of state When a substance changes state, the number of molecules in that substance doesn't change and so Your notes neither does its mass The only thing that changes is its energy Changes of state are physical changes and so they are reversible Melting & freezing Melting occurs when a solid turns into a liquid (e.g. ice to water) Freezing occurs when a liquid turns into a solid Boiling & condensing Boiling occurs when a liquid turns into a gas This is also called evaporating Condensing occurs when a gas turns into a liquid You need to know these four processes only, and the states at which they start and end. Examiner Tip It is very useful to think about water when learning the changes of state, because we are all used to the idea that solid water (ice) melts to become liquid water (water!) and boils to become gaseous water (water vapour). Page 3 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources However do remember that all substances undergo the same changes between the three states, but at different temperatures. So while water will help you to remember the names, don't refer to water in your answers unless it has been specified. Your notes Page 4 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Molecular Matter Your notes Arrangement & motion of particles All molecules and matter are in motion at room temperature The motion and arrangement of particles must be known for each state of matter In a solid: The molecules are very close together and arranged in a regular pattern The molecules vibrate about fixed positions In a liquid: The molecules are still close together (no gaps) but are no longer arranged in a regular pattern The molecules are able to slide past each other In a gas: The molecules are widely separated - about 10 times further apart in each direction The molecules move about randomly at high speeds Properties of states of matter State Solid Liquid Gas Density High Medium Low Arrangement of Regular pattern Randomly arranged Randomly arranged particles Movement of particles Vibrate around a fixed Move around each Move quickly in all position other directions Energy of particles Low energy Greater energy Highest energy The forces & distances between molecules Extended tier only Page 5 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Intermolecular forces and motion of particles The forces between molecules and matter (or 'particles') affect the state of matter Your notes This is because the magnitude of the forces affects the relative distances and motion of the particles This affects the ability of the substance to Change shape Change volume Flow The word particles can refer to: Atoms Molecules Ions Electrons Solids The molecules in a solid are held in place by strong intermolecular forces They only vibrate in position The distance between them is fixed and is very small This gives the solid its rigid shape and fixed volume Liquids The molecules in a liquid have enough energy to overcome the forces between them They are still held close together The volume of the liquid is the same as the volume of the solid Molecules can move around (by sliding past each other) This allows the liquid to change shape and flow Gases The molecules in a gas have more energy and move randomly at high speeds The molecules have overcome the forces holding them close together Page 6 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Because of the large spaces between the molecules The gas can easily be compressed and is also able to expand Your notes Gases flow freely Worked Example Two states of matter are described below. Identify each of the states of matter. Substance 1 molecules are spaced very far apart molecules move very quickly at random molecules move in a straight line Substance 2 molecules are quite closely packed together molecules move about at random molecules do not have fixed positions Answer: Substance 1 Step 1: Identify the distances between the molecules The molecules are spaced far apart This can only describe a gas Step 2: Identify the motion of the molecules The molecules move quickly, at random and in a straight line This confirms that substance 1 is a gas Substance 2 Step 1: Identify the distances between the molecules The molecules are closely packed This could describe either a solid or a liquid Step 2: Identify the motion of the molecules The molecules move at random and do not have fixed positions This confirms that substance 2 is a liquid Page 7 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Temperature & energy of particles As the temperature of a gas increases, so does the average speed of particles in the gas Your notes At higher temperatures, the particles have more kinetic energy The amount of pressure that a gas exerts on its container is dependent on the temperature of the gas This is because particles gain kinetic energy as their temperature increases There must, therefore, be a temperature at which the particles are stationary This is the lowest possible temperature, as particles cannot travel any slower than 0 m/s The temperature at which all particles are stationary is called absolute zero Absolute zero has a value of −273 °C Page 8 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Particle Model of Gases Your notes Motion of particles in a gas In the particle model, molecules in a gas are in constant random motion at high speeds Random motion means that the molecules are travelling in no specific path and undergo sudden changes in their motion if they collide: With the walls of its container With other molecules Pressure in a gas is caused by the collisions of particles with the walls of the container When the particles travel faster (e.g. at a higher temperature), they collide with walls more frequently This means the gas exerts a greater pressure Page 9 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Random motion of gas molecules in a container. Collisions with container walls creates pressure in the particle model Your notes Pressure & force of particles in a gas Extended tier only Gases fill their container The pressure is defined as the force per unit area F p= A Where: p = pressure in pascals Pa F = force in newtons N A = area in metres-squared m2 This equation and the particle model can be used to explain how particles exert pressure As the gas particles move about randomly they collide with the walls of their containers These collisions produce force at right angles to the wall of the gas container (or any surface) Pressure is force per unit area, so the force of these collisions exerts a pressure When the particles move faster, they have more frequent collisions with the container walls and these exert a greater force If the force exerted per unit area is greater and more frequent, the pressure exerted is also greater Page 10 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Gas molecules bouncing off the walls of a container exert a force perpendicular to the surface Page 11 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Brownian Motion Your notes What is Brownian Motion? The Kinetic Theory of Matter, which simply says that all matter is made up of tiny particles, was discovered almost by accident The Scottish scientist Robert Brown first described the random motion of pollen grains in water, which he saw under a microscope This observation could not be explained at the time, but later it was realised that it shows that substances are made of particles which are in constant motion (hence 'kinetic') Brownian Motion: the random motion of microscopic particles when observed through a microscope Brownian motion is the random movement of particles in a liquid or a gas produced by large numbers of collisions with smaller particles which are often too small to see When small particles (such as pollen or smoke) are suspended in a liquid or gas, they can be observed through a microscope moving around in a random, erratic fashion Explaining Brownian motion Extended tier only What is Brownian motion caused by? Page 12 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources When observing Brownian Motion, even with a microscope, only the microscopic particles can be seen Your notes The pollen or smoke particles are seen to move Smaller atoms and molecules, of water or air, are still too small to be seen These light, fast-moving atoms and molecules collide with the larger microscopic particles The collisions give the particles a little nudge, causing them to change their speed and directions randomly, each time they are struck by a molecule The presence of the light, fast moving atoms and molecules is inferred from the motion of the microscopic particles Inferences such as this are an important part of scientific investigation Light, fast-moving molecules collide with larger particles, giving them a little nudge Page 13 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes This not-to-scale diagram shows how the smaller, fast-moving particles (atoms and molecules) cause the larger, visible particles to move Page 14 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Gases & Absolute Temperature Your notes Absolute temperature What is absolute temperature? Temperature measured in kelvin is called absolute temperature The kelvin temperature scale begins at absolute zero 0 K is equal to -273 °C An increase of 1 K is the same change as an increase of 1 °C It is not possible to have a temperature lower than 0 K This means a temperature in kelvin will never have a negative value To convert between temperatures θ in the Celsius scale, and T in the Kelvin scale, use the following conversion: θ / °C = T / K − 273 T / K = θ / °C + 273 Page 15 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Conversion chart relating the temperature on the Kelvin and Celsius scales Worked Example Convert the following values between the Kelvin (absolute) and Celsius scales of temperature. a) 0 K = _______ °C b) 0 °C = _______ K c) 20 °C = _______ K Part (a) Step 1: Choose whether to add or subtract 273 to the value Page 16 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The question is in kelvin therefore subtract 273 to convert to Celsius Step 2: Do the calculation Your notes 0 − 273 = − 273 Step 3: Write the answer with units 0K = −273 °C Part (b) Step 1: Choose whether to add or subtract 273 to the value The question is in Celsius therefore add 273 to convert to kelvin Step 2: Do the calculation 0 + 273 = 273 Step 3: Write the answer with units 0 °C = 273 K Part (c) Step 1: Choose whether to add or subtract 273 to the value The question is in Celsius therefore add 273 to convert to kelvin Step 2: Do the calculation 20 + 273 = 293 Step 3: Write the answer with units 20 °C = 293 K The gas laws Pressure & volume (constant temperature) If the temperature of a gas remains constant, the pressure of the gas changes when it is: Compressed – decreases the volume which increases the pressure Expanded – increases the volume which decreases the pressure Page 17 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes At constant temperature, changing the volume changes the pressure Similarly, a change in pressure can cause a change in volume A vacuum pump can be used to remove the air from a sealed container The diagram below shows the change in volume to a tied up balloon when the pressure of the air around it decreases: Page 18 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes At constant temperature, changing the pressure changes the volume When a gas is compressed, the molecules will hit the walls of the container more frequently This creates a larger overall net force on the walls which increases the pressure Pressure & temperature (constant volume) Increasing temperature increases the pressure of a gas which is kept at a constant volume The average speed of molecules increases when the temperature increases (and vice versa) As the gas heats up, the molecules will travel at a higher speed They collide with the walls more often and with greater force, increasing the pressure Therefore, at a constant volume, an increase in temperature increases the pressure of a gas and vice versa Diagram A shows molecules in the same volume collide with the walls of the container more as the temperature increases Diagram B shows that since the temperature is directly proportional to the pressure (at constant volume), the graph is a straight line Page 19 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes At constant volume, an increase in the temperature of the gas increases the pressure due to more collisions on the container walls Boyle's Law Extended tier only Boyle’s law If the temperature T of an ideal gas is constant, then Boyle’s Law is given by: Page 20 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 1 p∝ V Your notes This means the pressure is inversely proportional to the volume of a gas This can also be written as: pV = constant The relationship between the pressure and volume for a fixed mass of gas at constant temperature can also be written as: p 1V 1 = p 2V 2 Where: p1 = initial pressure (Pa) p2 = final pressure (Pa) V1 = initial volume (m3) V2 = final volume (m3) Notice that volume and pressure are measured in m3 and Pa respectively In calculations if units are given in cm3 or MPa this is a rare case where calculations can be done using the original units as long as answers are reported in the same, original units and the final and initial units match Page 21 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Boyle's Law graph: Pressure is inversely proportional to volume Examiner Tip It is an easy mistake to make to think that an inversely proportional graph will be a straight line sloping downwards. After all, a directly proportional graph is a straight line (through the origin) which slopes upwards! The curve above which 'tends towards zero' (meaning the curve gets closer and closer but never touches the axis, or zero is an inversely proportional curve, as the graph below shows. Page 22 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 23 of 23 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers