particle model of matter Flashcards
what can the particle model be used to explain
- the different states of matter
- differences in density
density in solids
the particles are very close together so solids have a high density (high mass for their volume) - this is due to the strong forces of attraction between particles
density in liquids
the particles are still relatively close together so liquids have a relatively high density (high mass for their volume) - this is due to relatively strong forces of attraction between particles, but these are weaker than solids
density in gases
particles are very far apart so gases have relatively low density (low mass for their volume) - this is due to the negligible forces of attraction between particles
define internal energy
the energy stored inside a system by the particles (atoms and molecules) that make up the system
what happens when we heat a solid
we increase the internal energy of the system, and at one point, the solid undergoes melting and becomes a liquid
what happens when we heat a liquid
we increase the internal energy of the system, and at one point, the liquid undergoes boiling and becomes a gas
what happens when we cool a gas
we decrease the internal energy of the system, and at one point, the gas undergoes condensation and becomes a liquid
what happens when we cool a liquid
we decrease the internal energy of the system, and at one point, the gas undergoes freezing and becomes a solid
solid -> gas
sublimation
what happens when changes of state take place
mass is conserved; we do not add or take away any particles. however, the density of the object changes
what type of reaction are changes of state and why
physical and not chemical, because the material recovers its original properties if the change is reversed
what is internal energy the sum of
the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system
differences between evaporation and boiling
EVAPORATION:
- only the particles on the surface have enough energy to escape the liquid as a gas
- can take place below the boiling point
- slower process
- no bubbles produced
- leads to cooling
BOILING:
- occurs throughout the liquid
- faster process
- produces bubbles
- does not lead to cooling
on a heating and cooling graph, why does the temperature stop rising and become horizontal
the substance is undergoing a change of state; during this process, the heat is transferring energy to the potential energy stores of the particles but not the kinetic energy stores; the energy is being used to break the forces of attraction to change state, rather than to increase the temperature
what happens when we heat a substance
we change the energy stored within the system by increasing the energy of the particles that make up the system. this either raises the temperature of the system or produces a change of state
what does the increase in temperature of a system depend on
the mass of the substance heated, the type of material and the energy input to the system
define the melting point
the temperature at which a substance melts and freezes
define the boiling point
the temperature at which a substance boils and condenses
define latent heat
the energy needed for a substance to change state
define the specific latent heat of a substance
the amount of energy required to change the state of one kilogram of the substance with no change in temperature
define the specific latent heat of fusion
the amount of energy required to melt one kilogram of the substance with no change in temperature
e.g. it takes 334000J of energy to melt 1kg of ice, so that is its specific latent heat of fusion
(solid to liquid)
define the specific latent heat of vaporisation
the amount of energy required to boil one kilogram of the substance with no change in temperature
(liquid to vapour)
define the specific heat capacity of a substance
the amount of energy required to raise the temperature of one kilogram of the substance by one degree celsius
why does specific heat capacity fluctuate?
some substances require more energy to raise their temperature than others e.g. sand is usually hotter than the sea because water has a higher specific heat capacity (so more energy is needed to heat 1kg by 1 degree)
describe the molecules of a gas
the molecules of a gas are in constant random motion
describe how changing the temperature affects gas molecules
an increase in temperature increases the kinetic energy of the particles, which increases the number of successful collisions
what can you do to a gas (in relation to pressure) and what does this cause
a gas can be compressed or expanded by pressure changes; the pressure produces a net force at right angles to the wall of the gas container (or any surface)
define work
the transfer of energy by a force
what occurs when doing work on a gas
the internal energy of the gas increases and can cause an increase in the temperature of the gas
