paper 3 Flashcards
how has the atomic model changed overtime?
- dalton: small indestructible spheres, all atoms in an element are the same, atoms in one elemnt are different from another
- JJ. Thompson: discovery of negativley charged eletcron in all atoms, plum pudding model, over neutral
- Rutherford: tiny positivley charged nucleus (mass concentrated) , electrons round the outside
- Bohr: electrons can only move in fixed orbits (shells)
why do models change?
new evidnce brought up that cannot be explained using new models/ideas
describe the atom
- positivley charged nucleus
- surrounded by negativley charged electrons
- all mass in nucleus
- nuclear radius smaller than atom
what is the typical size of atoms and small moleucles
1 × 10^–10m
define density
how much mass is contined within a certain volume
what are the differences in density between a solid liquid and gas?
- in 1cm^3 there are more particles in a solid then in 1cm^3 of a gas
describe how mass is conserved when substances
melt, freeze, evaporate, condense or sublimate
- The law of conservation of mass states that you have to add or remove material for the mass of the system to change
how do physical changes differ from chemical changes?
- physical changes: particles are simply re-arranged and can recover it’s orginal properties if the change is reversed
- chemical changes are not easily irreversible
what are the effects of heating a system?
- energy stored within the system will increase, increase in temperature
- produce a change of state
- make chemical reactions happen
define the term specific heat capacity
the amount of energy needed to raise 1kg of a substance by 1kelvin
the lower the S.H.C the more easily it heats up
define specific latent heat of fusion
- the energy required to transfer 1kg of a substance from the solid state to the liquid state
(melting)
define specific latent heat of vaporisation
- the energy required to heat 1kg of a substance from liquid state to the gas state
(evaporation)
define temeperature
- the measure of the average kinetic energy of particles
how does the motion of a molecule of gas relate to the pressure?
- the more particles collide with the inside of the balloon (surface of container)
- producing a force with each collision, making an overall larger force
- exerted upon a certain area, gives rise to a pressure
how does the temperature of a gas relate to the pressure?
at constant volume
- more temperature
- particles have on average more kinetic energy
- collide more frequently with the walls of the container
- collsions produce a larger force over a given area
- producing a larger pressure
what is extrapolation?
extending the line of a graph, to estimate what would happen if you continue to change the independant variable
what happens when gases are compressed or stretched?
- the collsions of the gas particles produce a net force at right angles to any surface
what happens to the pressure of a gas when the volume is halved ?
at constant temperature
behaviour regarding particle
velocity and collisions
* double the number of collisions per second betwen the gas particles and container
* pressure doubles
how can doing work on a gas increase it’s temperature?
- energy transfered to the particles
- gain kinetic energy
- increase in their average energy, increase in energy
describe the earth’s atmosphere
an assumption of uniform
density
explain why atmospheric pressure
varies with height above the surface
of the planet
- atmospheric pressure decreases the higher you travel,
- as there are fewer gas particles
- becuase of a weaker gravitational field
why does a weather ballon expand as it rises?
appliccation Q
- travling higher mrans waker gravitational field
- so there will be less gas particles and a lower atomspheric pressure
- since there is a net outwards pressure (ballon pressure> atmospheric)
- the balloon expands
describe the force of upthrust
- there is a pressure differnce
- more presure is exerted at the bottom of the body, that at the top of the body
- net force upwards
what determines if a body sinks?
- if the weight force of the body is larger than the upthrust force (larger than the weight of the fluid displaced)