Entropy and feasibility of reactions Flashcards
how to tell if a reaction is endothermic
+ energy change
how to tell if a reaction is exothermic
- energy change
what is entropy (S)
- a measure of disorder
- amount of randomness in a system
why is S always positive
all substances possess a certain degree of disorder
what is the 2nd law of thermodynamics
in any spontaneous reaction, the total entropy increases.
General tendency towards disorder
what causes S to increase
more disorder
what is the standard entropy of a substance
the entropy content of 1 mole of that substance under standard conditions
J/K/mol
how to calculate standard entropy change of reaction
ΣS (product) – ΣS (reactants)
what would entropy be in this equation
C(s) + O₂(g) –> CO₂(g)
positive - more disorder
solid becomes gas
what would entropy be in this equation
2NO(g) + O₂(g) –> N₂O₄(g)
negative - less disorder
3 molecules become 2
How do you calculate Gibbs free energy (G)
ΔG = ΔH - T ΔS
How to tell if a reaction is feasible using ΔG
negative = feasible
positive = not feasible (at that temp)
what does it mean if ΔG = 0
system is at equilibrium
