5.2.2 Enthalpy and Entropy Flashcards
what is entropy?
- a measure of the dispersal of energy in a system or the degree of disorder
- S
what is a system?
particles involved in the reaction
what is disorder?
spreading out/randomness
what is standard entropy?
entropy of one mole of a substance under standard condtions
what are the units for entropy?
JK-1mol-1
why is S always positive?
all substances must have some degree of disorder
what is the link between disorder and entropy?
- particles spread out
- more disordered
- increase in entropy
- positive delta S
examples of delta S increasing
- changes of state from solid -> liquid -> gas
- dissolving a solid
- reactions involving an increase in the number of moles of gas (always count moles of gas on each side)
how to calculate the change in entropy?
change in entropy = entropy of products - entropy of reactants
if delta S is positive…
the system has become more disordered
if delta S is negative…
the system has become less disordered
what is a feasible reaction?
if the chemical system becomes more stable and its overall energy decreases
what contributes to Gibbs free energy?
results from
- enthalpy change
- entropy change
- temperature (K)
what is the equation linking free energy, entropy and enthalpy?
delta G = delta H - TdeltaS
(JK-1mol-1 / 1000)
what is Gibbs free energy?
- determines the feasibility of a reaction
- represents the ‘driving force’ that determines whether a chemical reaction will happen or not
- for a reaction to be feasible (spontaneous) delta G must be negative -> overall energy decreases = more stable
