2. Entropy Flashcards
what does entropy tell us
how much disorder there is
what is entropy a measure of
the number of ways that particles can be arranged and the number of ways that the energy can be shared out between the particles
what does a large positive value of entropy show
a high level of disorder
the more disordered the particles, the higher the entropy
the two things that effect entropy
- physical state
2. more particles
how does physical state affect entropy
solids have the lowest entropy (particles wobble around a fixed point, hardly any randomness)
gas have the highest entropy (most random arangement of particles)
how does more particles affect entropy
more particles more entropy
(more particles more ways they and their energy can be arranged)
e.g. N2O4(g) -> 2NO2 entropy increase, number of moles increased
why do particles move to try increase their entropy
substances are more energetically stable when theres more disorder
why are some reactions feasible (happen by themselves without addition of energy) even when the enthalpy change is endothermic (△H+ve)
substances are more energetically stable when theres more disorder so particles move to try increase their entropy
e.g. why is the reaction between sodium hyrdrogencarbonate and hydrochloric acid feasible even though it is endothermic
NaHCO3(s) + H+(aq) -> Na+(aq) + CO2(g) + H2O(l)
increase in entropy
reaction produces CO2 gas and H2O liquid
liquids and gas are more disordered than solids and have a higher entropy.
the increase in entropy overcomes the change in enthalpy
(also favoured because there is an increase in moles)
when a substance reaches its maximum entropy state (its lowest energy state) its said to be
thermodynamically stable (it wont react any further without the input of energy)
calculating the entropy change of a reaction
equation
△S = Sproducts - Sreactants
entropy of products - entropy of reactants
calculating the entropy change of a reaction
units
J K-1 mol-1
Reactions with a positive entropy change are more likely to be _____
feasible
a negative entropy change DOES NOT guarantee
the reaction cant take place/ wont be feasible.
other factors enthalpy, temperature and kinetics involved
