states of matter - phases Flashcards
(32 cards)
describe attraction/repulsion in gases, liquids and solids
gas - repulsive force > attractive force
liquid - attractive > repulsive, so net attractive
solid - maximum attractive force
what are the 3 possible motions of particles?
translational, vibrational, rotational
how do changes in temp and pressure affect state of molecules?
increasing temperature = increasing kinetic energy -> gas
increasing pressure = increasing impact of IMF as distance decreases -> solid
phase definition
a homogenous part of a system - physically and chemically uniform, separated from other phases by phase boundaries
how many phases do gases have?
only 1 single phase, no matter how many components are present
how many phases do liquids have?
for a single compound there is only 1 phase
if there are multiple compounds phases depend on how well they mix
e.g. water + ethanol completely mix so 1 phase
water + organic solvent do not mix so 2 phases
how many phases do solids have?
a single component can have multiple phases, depends on how many structures it can adopt
give the 6 processes that transform gases, liquids and solids
solid > liquid = melting
liquid > solid = freezing
gas > liquid = condensation
liquid > gas = evaporation
solid > gas = sublimation
gas > solid = reverse sublimation
what do lines on a phase diagram represent?
phase boundaries
on these lines, the processes that transform states/phases occur, and the 2 neighbouring states will be in dynamic equilibrium (only place where this is possible
define triple point
the point on a phase diagram representing the conditions at which all 3 phases can exist simultaneously
what is supercritical fluid?
fifth natural state - substances flow like a gas and solvate like a liquid
separated from other phases by dashed lines/ no lines, these are critical boundaries (not really proper phase boundaries
define critical point
the point on a phase diagram representing where phases become supercritical / where phase boundaries meet critical boundaries
how do solids and liquids differ in density? + give an exception
normally solids are denser than their own liquids, this means they will sink
exception = ice and water
why is ice less dense than water?
hydrogen bonding ability of water gives ice an open lattice-like structure, meaning it can float on the surface of water
what makes the phase diagram of water strange?
as ice is less dense than water, water molecules are closer in liquid form, which causes its liquid/solid phase boundary to have a backwards slope on its phase diagram , meaning at high pressure water becomes liquid, not solid
kinetics vs thermodynamics - what do these laws tell us about reactions?
kinetics tells us how fast a reaction will take place
thermodynamics tells us whether or not a reaction can take place and how far it will go
meta stable definition
when reactions are possible/compounds are unstable but the reaction/decomposition occurs so slowly that it is insignificant/cannot occur for very large amounts of time under standard conditions
vapour pressure definition
the pressure of a vapour when it is in equilibrium with its condensed phase
how does vapour pressure relate to boiling point?
the temperature at which vapour pressure - atmospheric pressure = the boiling point
how can phase diagrams be used to plot heating/cooling curves?
changing/increasing the temperature at a fixed pressure, allows points/temps at which melting, etc occurs to be plotted
what does a heating curve look like at melting/boiling points?
the temperature remains constant until all substance has changed state, so gradient =0
what do the gradients of the slops of heating curves represent?
heat capacity
heat capacity definition
energy needed to heat 1g of a substance by 1K
units = J K^-1g^-1
2 types of heat capacity
Cp = heat capacity at constant pressure
Cv = heat capacity at constant volume
Cp =/= Cv
