R1.4 Entropy and spontaneity Flashcards
entropy (S)
a measure of the dispersal or distribution of matter and/or energy in a system
entropy is higher
the more ways the energy/matter can be distributed
under the same conditions, which state has the greatest entropy
gas>liquid>solid
comment on the entropy and disorder of a solid
low
comment on the entropy and disorder of a gas
high
entropy of a perfectly ordered crystal at 0K, explain this entropy
entropy = 0
there is only one way to organise it
microstate / microscopic state
each of the possible arrangements
is entropy positive or negative, explain
positive
everything has entropy (apart from a crystal at 0K)
2nd law of thermodynamics
in every process, the total entropy of an isolated system always increases
what does the 2nd law of thermodynamics tell us
it is far more likely for the universe to tend towards disorder than it is to miraculously order itself
spontaneous reactions, comment on their entropy
overall increase in entropy
overall entropy of universe unchanged
system at equilibrium
negative entropy change
reverse process is spontaneous
entropy of products > entropy of reactants
change in entropy = positive
entropy of reactants > entropy of products
change in entropy = negative
low entropy value example
solid at low temperature
regularly arranged lattice
high entropy value example
gas at high temperature
larger molecule has…
more entropy
entropy of a closed system can…
remain fixed or increase
a spontaneous reaction is one…
which moves to completion with no external intervention
Gibbs free energy
is used to work out if a reaction is feasible at a certain temperature
feasibility
the likelihood of a reaction to occur
temperature affect this
Gibbs free energy in a feasible reaction
negative
Gibbs free energy is a measure of
how much energy there is in a system and how feasible a reaction is
change in entropy is a measure of
how energy/matter spreads out over a course of reactions
what do we want in terms of entropy and enthalpy
- maximise entropy: things like to be spread out
- minimise enthalpy: things like to be low energy, more stable
link between feasibility and temperature
feasibility increases with temperature
at a constant pressure, a change is spontaneous if…
change in Gibbs free energy is negative
what happens to Gibbs free energy as a reaction approaches equilibrium
Gibbs free energy becomes less negative and finally reaches zero
