P6 Molecules and matter. Student Book answers. P6.1 Density. Question Answer Marks Guidance. 1 a m 3 (= 0.80 m 0.60 m 0.

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1 P6. Density a m 3 (= 0.80 m 0.60 m 0.05 m) b = 2500 kg/m 3 2 a 36 g 48 g = 88 g 2 b =. g/cm 3 3 a i m 3 (= 0.0 m m 0.05 m) 3 a ii = kg/m 3 3 b v = = m 3 thickness t = = m or mm 4 Use top pan balance to measure mass of bolt, fill measuring cylinder half-full of water and measure volume of water in it, tie bolt on thread and gently lower fully into water, volume of bolt given by rise in level of water in measuring cylinder, use density = to calculate density of bolt from its mass and volume Oxford University Press This resource sheet may have been changed from the original.

2 P6.2 States of matter a i vaporisation a ii freezing a iii melting b same mass of ice cube and water in beaker after ice cube has melted, density = mass per unit volume so if volume of ice cube > volume of melted water, density of ice < density of water 2 a condensation 2 b evaporation/vaporisation 2 c melting 2 d freezing 3 a particles start to move about at random, no longer in fixed positions 3 b particles in water vapour move at random and not in contact with each other except when they collide, when water vapour condenses on a cold surface, vapour particles lose energy when they collide with surface and stay on surface as a film of liquid, particles in film move at random in contact with each other 4 particles in gas much more energetic and move faster and spaced further apart than particles in solid or liquid, for given mass of gas, particles occupy much greater volume than equal mass of same substance in liquid or solid state, density = mass / volume, density of gas much less than density of same substance as liquid or solid Oxford University Press This resource sheet may have been changed from the original. 2

3 P6.3 Changes of state boiling takes place at a certain temperature whereas evaporation occurs from a liquid at any temperature, boiling takes place throughout liquid whereas evaporation from surface only, evaporation can cause liquid to cool whereas boiling does not 2 a i graph with suitable scales, correctly plotted points, best fit line with flat section from 50 s to about 240 s 2 a ii 79 C 2 b 60 C: solid, at 79 C: begins to melt, after 90 s all melted and liquid temperature then rises to above 90 C 3 salt and water form solution which will not freeze unless temperature drops below freezing point of solution, so no ice forms on road unless temperature drops below freezing point, if solution does freeze, grit provides friction between tyres and ice to help stop vehicles sliding 4 particles move randomly in contact with each other as temperature falls from 80 C to 75 C, as temperature falls particles lose energy and move more slowly until at 75 C they stop moving around and substance changes from liquid to solid, at 75 C particles become fixed in position and vibrate, once all substance has changed state, temperature falls from 75 C to 70 C and vibrations of particles less vigorous Oxford University Press This resource sheet may have been changed from the original. 3

4 P6.4 Internal energy a particles in a gas move at high speed in random directions, colliding with each other and with internal surface of container, pressure on solid surface caused by force of impacts of gas particles with surface b when solid heated to its melting point particles gain KE and vibrate more about fixed positions, at melting point, particles gain enough energy to break away from each other and move about, molecules that break free are in liquid state as they move about in contact with each other 2 a liquid: particles close together and move about, not in fixed positions 2 b gas: particles far apart and move about 2 c solid: particles vibrate about fixed positions and close together 2 d does not exist: particles that vibrate about fixed positions are in solid and not far apart 3 internal energy transferred to solid at its melting point gives molecules enough energy to overcome strong forces of attraction holding them together in solid structure, PE increases as particles break free from each other Oxford University Press This resource sheet may have been changed from the original. 4

5 4 heat energy transferred by heating from warm water to ice, water cools and water particles move more slowly so they lose KE, ice melts because it gains internal energy and particles in ice gain enough PE to break free from each other, when ice melts, melted water from ice and warm water mix so molecules from the ice, on average, gain KE and molecules from warm water lose KE Oxford University Press This resource sheet may have been changed from the original. 5

6 P6.5 Specific latent heat a kg kg = kg b = 340 kj/kg 2 m w = 0.52 kg 0.44 kg = kg L = = 2.3 MJ/kg 3 a E = (5 9) C = 3024 J 3 b E 2 = = 302 J 3 c energy transferred to melt ice = = 2722 J specific latent heat of fusion of water = = 340 kj/kg 4 E = 0.00 kg 2.25 MJ/kg = J t = = 75 s Oxford University Press This resource sheet may have been changed from the original. 6

7 P6.6 Gas pressure and temperature a increases b unchanged c increases 2 smoke particles move at random due to random impacts of air molecules, if gas temperature increases, gas molecules move faster on average so impacts are harder and of impacts per second increases, so smoke particles move faster 3 gas pressure stops increasing (or decreases) when valve opens, of gas molecules in cylinder decreases, so of impacts they make per second on cylinder s internal surface decreases and gas pressure stops increasing (or decreases) 4 a unless water is stirred, (hot water rises and so) temperature of water differs in beaker, thermometer does not measure average temperature of water 4 b air in flask before sealed at atmospheric pressure, so pressure gauge reads atmospheric pressure before it is sealed Oxford University Press This resource sheet may have been changed from the original. 7

8 P6.7 Gas pressure and volume volume increases and pressure decreases 2 a = m 3 2 b 2 c 2 d = Pa = m 3 = Pa 3 initial volume V = ( ) cm 3 = 20 cm 3, final volume V 2 = 00 cm 3 = 20 kpa 4 to reduce volume of air in cylinder, force must be applied to piston to overcome force of air pressure in cylinder, WD on air by applied force, so internal energy of trapped air increases, temperature of air increases, as compression rapid very little energy transfer to surroundings takes place Oxford University Press This resource sheet may have been changed from the original. 8