P6

Question 1

what is the equation to work out density

Answer 1

mass/ volume

Question 2

what kinds of objects float on water

Answer 2

ones with a lower density than water (less than 1000 kg/m^3)

Question 3

what is a physical change

Answer 3

when no new substances are formed

Question 4

what is the conservation of mass law

Answer 4

when a substance changes state, the mass stays the same because the number of particles stays the same

Question 5

why is salt added to grit used to grit the roads

Answer 5

adding salt to water lowers the melting point as it is an impurity- means that roads don’t get icy until they are colder

Question 6

what happens whilst a pure substance is changing its state

Answer 6

the temperature doesn’t change at all

Question 7

what is latent heat

Answer 7

the energy transferred to a substance when it changes state

Question 8

when and where does evaporation of a liquid happen

Answer 8

on the surface of the liquid when it is below it’s boiling point

Question 9

what does it mean when water boils

Answer 9

molecules have gained enough energy to move away from each other so the water has turned into steam

Question 10

what is internal energy

Answer 10

the sum of the kinetic and potential energy stores in the particles of a substance caused by their individual motions and positions

Question 11

what does internal energy not include

Answer 11

gpe or ke casued by the motion of the whole substance

Question 12

what is the specific heat capacity equation

Answer 12

change in energy = mass x specific heat x temp change

Question 13

3 points about the particles in solids

Answer 13

1. strong forces of attraction between the particles which bond the particles in fixed positions
2. each particle vibrates around an average, fixed position
3. when a solid is heated, the particle’s energy store is increased so they vibrate more. sometimes the solid melts if the particles have gained enough energy to break away from the structure

Question 14

how are the particles of a liquid different to a solid

Answer 14

1. they have weaker forces of attraction that are not strong enough to hold them together in a rigid structure
2. the forces are strong enough to stop the particles moving away from each other completely at the surface
3. when a liquid is heated, some of the particles gain enough energy to break away from the other particles so these molecules are in gas state above the liquid

Question 15

how are gas particles different to solids and liquids

Answer 15

1. forces of attraction are so weak they are insignificant
2. move about at high speed in random directions, colliding with each other and the internal surface of their container
3. when heated particles gain ke and move faster which causes pressure to increase

Question 16

what is specific latent heat of fusion

Answer 16

the energy needed to change 1kg of the substance from solid to liquid at its melting point (without changing the temperature)

Question 17

what is the specific latent heat of fusion equation

Answer 17

Lf (J/kg) = energy/ mass

Question 18

what is the specific latent heat of vaporisation

Answer 18

energy needed to change 1kg of the substance from liquid to vapour at its boiling point (without changing the temp)

Question 19

what is the specific latent heat of vaporisation equation

Answer 19

Lv (J/kg) = energy/mass

Question 20

why should you never heat food in a sealed can

Answer 20

as the temp increases the pressure of the gas increases and so the can could explode

Question 21

why does increasing the temperature of a sealed gas container increase the pressure of the gas inside

Answer 21

ke of molecules increases so speed of molecules increases and the molecules hit the container surface more often and with more force which increases pressure

Question 22

why can temp of a gas increase if it is compressed rapidly

Answer 22

work is done on it and the energy isn’t transferred quickly enough to its surroundings

Question 23

why does gas pressure increase if the volume of a fixed mass of gas is reduced

Answer 23

1. the space the molecules move in is smaller so they don’t travel as far between each collision
2. the molecules hit the surface more often

Question 24

what is boyle’s law

Answer 24

pressure x volume is constant

for a fixed mass of gas at constant temperature : pressure x volume = constant