chem1046: free energy & thermodynamics

true or false: fast & slow determine the spontaneity of a reaction

false

spontaneous energy diagram

long on the “exit”, product ends lower than reactant, looks like exothermic graph.

trait of exothermic energy graph

has less potential energy after the reaction

exothermic

heat on the “exit”/product side, almost always spontaneous

state function

properties that do not depend upon the path followed & only depend upon initial and final state. example: entropy, potential energy

relation to enthalpy 

negative: exothermic, positive: endothermic

true or false? decrease in enthalpy doesn’t ALWAYS mean a process is spontaneous

true

true or false? spontaneous processes are NOT irreversible/they can be reversed

false, because there is a net release of energy when it proceeds in that direction, will only proceed in one direction

2nd law of thermodynamics

for any spontaneous reaction, the entropy of the universe increases.

delta s_univ>0

processes that increase the entropy of the universe occur naturally

entropy and spontaneity 

if delta s is positive: spontaneous

if delta s is neg: non-spontaeous

free energy (deltaG)

ultimate deciding factor for the spontaneity of a reaction.

the energy to do work

if neg: spontaneous, if pos: non-spontaneous

free energy equation

deltaG = deltaH - (T)(deltaS)

true or false? entropy increases with more molecular complexity

false, more configurations hinting less entropy

deltaH is neg, deltaS is pos

always spontaneous

deltaH is pos, deltaS is neg

never spontaneous

deltaH is neg, deltaS is neg

small T to be spontaneous

deltaH is pos, deltaS is pos

high T to be spontaneous

entropy (s)

thermodynamic function that increases as the # of equivalent ways of arranging the components increases

microstate (W)

number of equivalent ways a system can be arranged

equation for microstate

W = (ways of orientation)^{# of particles}

equation for entropy (s)

entropy (s) = k ln W (k=1.38 × 10^-23)

initial and final entropy

initial: s_i = k ln W_i

final: s_f = k ln W_f

change in entropy equations

original equation: deltaS = s_f - s_i

derived equation: k ln W_f / W_i

deltaS rxn equation

deltaS rxn = entropy of products - entropy of reactants

deltaS rxn = (cS_C + dS_D) - (aS_A + bS_B)

what does negative entropy of a reaction mean?

this means negative means entropy is going DOWN, so the reaction is non-spontaneous

entropy equation for change in state:

deltaS = -deltaH/T

entropy equation for temp change & no state change:

deltaS = nC_p ln (T₂ / T₁)

(C_p is 29 J/(mol x k) )

free energy/thermodynamics standard conditions:

T = 25 degrees Celsius

P = 1 atm

Concentrations = 1 M

non-standard condition (given)

deltaG = deltaG^o + RT lnQ

(R = 8.314 J/mol x K, deltaG^o = standard free energy, Q = reaction quotient)

at equilibrium, or deltaG^o = 0,

the reactions are in the same rate resulting in no change in the system’s energy.

equation at equilibrium

deltaG^o = -RTlnK

chemical equilibrium

Qc < Kc system proceeds from left to right to reach equilibrium

Qc = Kc the system is at equilibrium

Q_c > Kc system proceeds from right to left to reach equilibrium