Block 2: Thermodynamics & Equilibrium Flashcards
(16 cards)
What are the differences between chemical phases & species
Phases are physically distinct, mechanically separable, homogeneous in composition (all gas, all solid, etc.), & observable with the naked eye or a microscope
Species are entities distinguishable by molecular formulas & structures & are measured in chemistry
What conditions exist under chemical equilibrium?
The rates of forward and reverse reactions in a closed system are equal, so concentrations of reactants and products are consistent over time
What is the first law of thermodynamics?
Energy cannot be created or destroyed; chemical reactions merely redistribute atoms & their bonds, the latter of which dictate changes in relative energy
What are exothermic & endothermic reactions?
Exothermic reactions experience the loss of heat (enthalpy) from a system
Endothermic reactions experience the addition of heat to a system
How is change in enthalpy calculated?
By subtracting the sum of the formation energies of all reactants from the sum of the formation energies of all products
What is formation energy & how is it measured?
The energy change occurring when a compound is formed is measured experimentally or estimated from the sum of bond energies. Formation energy of all free atoms is 0
What is the 2nd law of thermodynamics? What does this imply about the universe?
Entropy (randomness) increases over time. The universe’s entropy is inherently >0
How does enthalpy relate to entropy?
Change in enthalpy is the expression of entropy change at universal level; loss of heat to surroundings results in the universe’s positive entropy
What is Gibbs Free Energy & how is it calculated?
GFE describes the overall enthalpy & entropy changes in a reaction & determines whether a reaction requires energy input (endergonic) or releases free energy (exergonic)
∆G = ∆H - T∆S (equation for GFE at a given temperature. A different equation is used for actual concentrations)
In which directions are exergonic & endergonic reactions spontaneous & do they favour products or reactants?
Exergonic (∆G<0) reactions are spontaneous forwards & favour products
Endergonic (∆G>0) reactions are spontaneous backwards & favour reactants
What does the equilibrium constant express?
Keq represents the relative abundance of a reaction’s products & reactants at equilibrium
How does Keq represent the concentration of a reaction?
Keq < 1 reactions produce more reactants than products at equilibrium
Keq = 1 reactions produce an equal ratio of reactants to products at equilibrium
Keq > 1 reactions produce more products than reactants at equilibrium, typically running to completion
What does the reaction constant represent?
Q represents the relative abundance of a reaction’s products & reactants outside of equilibrium
Q = Keq systems are at equilibrium
Q < Keq systems shift toward products to reach equilibrium
Q > Keq systems shift towards reactants to reach equilibrium
How do ∆G, Keq, & Q relate?
∆G describes the free energy of a reaction at current conditions & determines spontaneity & immediate direction
Keq describes the ratio of reactants & products at equilibrium & determines where the reaction will end up & whether products & reactants are favoured in the long run
Q describes the ratio of reactants & products at a given moment & determines the direction of the shift required to reach equilibrium
What does the Van’t Hoff equation represent?
Changes in Keq with temperature
What factors does thermodynamics show & what factors does it not show?
Thermodynamics shows the direction a reaction is heading & the potential final state of a system but does not show its mechanism or rate
