Cambridge CIE IGCSE Chemistry Past Paper PDF

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Your notes Chemistry Solids, liquids & gases Contents Kinetic Theory States of Matter Pressure & Temperature in Gases Diffusion...

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Your notes Chemistry Solids, liquids & gases Contents Kinetic Theory States of Matter Pressure & Temperature in Gases Diffusion Page 1 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Kinetic Theory Your notes Solids, liquids & gases Solids Solids have a fixed volume and shape and 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 Liquids Liquids also have a fixed volume but adopt the shape of the container They are generally less dense than solids (an exception is water), but much denser than gases The particles move and slide past each other which is why liquids adopt the shape of the container and also why they are able to flow freely Gases Gases do not have a fixed volume, and, like liquids, take up the shape of the container Gases have a very low density Since there is a lot of space between the particles, gases can be compressed into a much smaller volume The particles are far apart and move randomly and quickly (around 500 m/s) in all directions They collide with each other and with the sides of the container (this is how pressure is created inside a can of gas) Summary of the properties of solids, liquids and gases Solid Liquid Gas Page 2 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Diagram Your notes Arrangement of Regular arrangement Randomly Randomly arranged particles arranged Movement of Vibrate about a fixed position Move around each Move quickly in all particles other directions Closeness of Very close Close Far apart particles Density High Medium Low Energy of Low energy Greater energy Highest energy particles Examiner Tips and Tricks You can explain the differences in the physical properties of solids, liquids and gases by referring to the arrangement and motion of particles. This is called the kinetic theory of matter. Page 3 of 18 © 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 State changes State changes occur when: Solids become liquids Liquids become gases Gases become liquids Liquids become solids Each state change requires a change in the energy, arrangement and movement of the particles The state changes Page 4 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The inter-conversions / state changes are shown in relation to energy Melting Melting is when a solid changes into a liquid Requires heat energy which transforms into kinetic energy, allowing the particles to move 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 exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same. Water, for example, freezes and Page 5 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources melts at 0 ºC Requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature Your notes Boiling Boiling is when a liquid changes into a gas Requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and within the liquid Occurs at a specific temperature known as the boiling point (b.p.) Evaporation Evaporation occurs when a liquid changes into a gas and occurs 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. of the liquid The larger the surface area and the warmer the liquid surface, the more quickly a liquid can evaporate Condensation Condensation occurs 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 Examiner Tips and Tricks Questions on the particle theory of matter show interconversion of states with a reversible arrow: ⇌, which means that the process can go forwards and backwards. Read the question carefully and pick the direction of the change in state that the question refers to. State changes & kinetic theory Extended tier only When substances are heated, the particles absorb thermal energy which is converted into kinetic energy This is the basis of the kinetic theory of matter Page 6 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Heating a solid causes its particles to vibrate more As the temperature increases, the particles vibrate so much that the solid expands until the Your notes structure breaks This is when the solid melts into a liquid Heating a liquid causes its particles to move more and spread out Some particles at the surface gain sufficient energy to overcome the intermolecular forces This is when a liquid starts to evaporate When the boiling point is reached, all of the particles gain enough energy to escape and the liquids boils into a gas These changes in state can be shown on a graph called a heating curve: A heating curve showing the states, state changes and temperature changes as time progresses Cooling down a gas has the reverse effect and this would be called a cooling curve: Page 7 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A cooling curve is like a heating curve, but is the mirror image Heating and cooling curves are used to show how changes in temperature affect changes of state The horizontal sections occur when there is a change of state but there is no change in temperature Page 8 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Pressure & Temperature in Gases Your notes Pressure & temperature in gases A change in temperature or pressure affects the volume of gases As the air inside a hot air balloon is heated up, it expands and the balloon gets bigger This is because the volume of a gas increases as temperature increases As temperature increases gas volume increases. The density decreases as the volume increases so the balloon rises. Page 9 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources If you have a gas stored inside a container that is squeezed, the pressure increases as you decrease the volume Your notes This is what happens in a bicycle pump Pressure increases as volume decreases in a bicycle pump As you compress the bicycle pump, the high pressure allows you to inflate a tyre You can feel the force of the high pressure if you put your finger on the end of the pump Gases & kinetic theory Extended tier only Gaseous particles are in constant and random motion The pressure that a gas creates inside a closed container is produced by the gaseous particles hitting the inside walls of the container: Page 10 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Moving particles of gas colliding with each other and the container walls How does temperature affect the volume of a gas? Increasing the temperature increases the kinetic energy of each particle Remember: The thermal energy from increasing the temperature is converted to kinetic energy in the particles As the temperature increases, the particles in the gas move faster and spread out more If the gas particles are inside a container, they will collide with the container walls more frequently If the container walls are flexible and stretchy then the container will get bigger and bigger, just like the hot air balloon! Examiner Tips and Tricks If you are talking about the particles, then make sure that you talk about them spreading out. If you are talking about the material, then you can use the word expand. You will lose a mark in an exam if you talk about particles expanding! Page 11 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources How does pressure affect the volume of a gas? Pressure is about the number of particles in a given volume Your notes Increasing the pressure means that there are the same number of particles but in a smaller volume Conversely, decreasing the pressure means that there are the same number of particles but in a larger volume When the pressure increases, the volume decreases. This means that the molecules collide with the container walls more frequently Since the volume is decreased, the gas particles hit the container walls more frequently If the pressure is too high, this can result in the container leaking gas or exploding Page 12 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Diffusion Your notes Diffusion Diffusion occurs in gases and liquids, due to the random motion of their particles It is where particles move from an area of high concentration to an area of low concentration Eventually the concentration of particles is even as the particles are evenly spread throughout the available space Diffusion happens on its own and no energy input is required Although, it occurs faster at higher temperatures because the particles have more kinetic energy Diffusion in liquids Potassium manganate(VII), KMnO4 , in water is a typical demonstration of diffusion in liquids: Page 13 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 14 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Diffusion of potassium manganate(VII), KMnO4 , in water. After a few hours, the concentration of KMnO4 is the same throughout the solution Diffusion in gases Diffusion is faster in gases than in liquids This is because gaseous particles have more energy and move quicker than liquid particles For example, the diffusion of bromine gas and air: Page 15 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Bromine diffuses until it is evenly spread throughout the container At the start, the orange-brown bromine gas is an area of high concentration It diffuses from a high to low concentration After 5 minutes, the bromine gas will have diffused from the bottom jar until it is evenly spread throughout both jars The same can be said for the air, although it is less obvious as it is colourless Examiner Tips and Tricks When you are talking about diffusion, you should (where appropriate) include: Ideas about areas of high and low concentration The energy / movement of the particles Diffusion & molecular mass Page 16 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Extended tier only How molecular mass affects diffusion Your notes At the same temperature, different gases do not diffuse at the same rate. This is due to the difference in their relative molecular masses Gases with a lower relative molecular mass are "lighter" which means that they: Travel faster Travel further in the same amount of time The reverse argument is true for gases with a high relative molecular mass, they: Travel slower Do not travel as far in the same amount of time For example, the reaction between ammonia and hydrogen chloride Diffusion of ammonia and hydrogen chloride Ammonia gas and hydrogen chloride gas react together to form solid ammonium chloride NH3 (g) + HCl (g) → NH4Cl (s) The Mr of ammonia is 17, while the Mr of hydrogen chloride is 36.5 This means that ammonia will travel faster and further than hydrogen chloride Therefore, the ammonium chloride will form nearer to the hydrogen chloride This is seen as a white "smoke" ring inside the gas tube Page 17 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Ammonia molecules have less mass than HCl molecules so they diffuse faster and the product forms closer to the HCl end Page 18 of 18 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers