P6 Flashcards
what is the equation to work out density
mass/ volume
what kinds of objects float on water
ones with a lower density than water (less than 1000 kg/m^3)
what is a physical change
when no new substances are formed
what is the conservation of mass law
when a substance changes state, the mass stays the same because the number of particles stays the same
why is salt added to grit used to grit the roads
adding salt to water lowers the melting point as it is an impurity- means that roads don’t get icy until they are colder
what happens whilst a pure substance is changing its state
the temperature doesn’t change at all
what is latent heat
the energy transferred to a substance when it changes state
when and where does evaporation of a liquid happen
on the surface of the liquid when it is below it’s boiling point
what does it mean when water boils
molecules have gained enough energy to move away from each other so the water has turned into steam
what is internal energy
the sum of the kinetic and potential energy stores in the particles of a substance caused by their individual motions and positions
what does internal energy not include
gpe or ke casued by the motion of the whole substance
what is the specific heat capacity equation
change in energy = mass x specific heat x temp change
3 points about the particles in solids
- strong forces of attraction between the particles which bond the particles in fixed positions
- each particle vibrates around an average, fixed position
- 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
how are the particles of a liquid different to a solid
- they have weaker forces of attraction that are not strong enough to hold them together in a rigid structure
- the forces are strong enough to stop the particles moving away from each other completely at the surface
- 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
how are gas particles different to solids and liquids
- forces of attraction are so weak they are insignificant
- move about at high speed in random directions, colliding with each other and the internal surface of their container
- when heated particles gain ke and move faster which causes pressure to increase
what is specific latent heat of fusion
the energy needed to change 1kg of the substance from solid to liquid at its melting point (without changing the temperature)
what is the specific latent heat of fusion equation
Lf (J/kg) = energy/ mass
what is the specific latent heat of vaporisation
energy needed to change 1kg of the substance from liquid to vapour at its boiling point (without changing the temp)
what is the specific latent heat of vaporisation equation
Lv (J/kg) = energy/mass
why should you never heat food in a sealed can
as the temp increases the pressure of the gas increases and so the can could explode
why does increasing the temperature of a sealed gas container increase the pressure of the gas inside
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
why can temp of a gas increase if it is compressed rapidly
work is done on it and the energy isn’t transferred quickly enough to its surroundings
why does gas pressure increase if the volume of a fixed mass of gas is reduced
- the space the molecules move in is smaller so they don’t travel as far between each collision
- the molecules hit the surface more often
what is boyle’s law
pressure x volume is constant
for a fixed mass of gas at constant temperature : pressure x volume = constant
