Question

(a) For overall chemical reactions that describe an equilibrium condition or balance between reactant and product species, explain why thermodynamic equilibrium constants cannot be determined solely from the ratios of forward and backward rate constants.

(b) Why is it required for chemical reactions to be balanced in both mass and charge in order to apply thermodynamic principles (i.e., equilibrium constants or free energies of reaction)?

Answer 1

a)

equilbrium is always present in reactions, they always tend to form due to forces/interaciton sin the natural balances.

There is no 100% or 0% conversions, at the smallest level, there is always some equilbirium.

Now, consider a ratio between: reactants and product

K = [products]^p / [Reactants]^r

Theromdinamically, recall that we can get K via free energy

free energy is a concept which gomes form the 2nd law of thermodynamcis, using the concept that the universe always increases in entropy.

dG = dH - T*dS becomes true, and a spontaneous process must be always dG < 0

this means that

dG = -RT*ln(Keq)

therefore a Keq! > 1; which implies products > reactants, will have enough free nergy to occur (negative dG value)-

.Also note that this is about thermodynamics

We also care about "time" if this is done in a long time, relatively speaking, then we assume the reaciton does not occur, since it will take 4 billion years ( for instance )

Then,

forward rate constant vs. backwards rate constants can be overall added:

if Kforward = Kreverse, this is assumed to be in equilbirium, no reaciton occurs

if Kforward > Kreverse, this will eventually happen

if Kforward >> Kreverse, this will occur rapidly

and so on.

B

note that:

ther eis conservation of energy AND mass

For mass --> it contains charge typically in the form of protons, or electrons, they will not dissapear ( unless they are nuclear reacitons, which then transfor into energy)

The charge will always be balanced in a chemical reaction.

electrons initially = electrons at the end

protons initially = protons at the end

neutrons initially = neutrons at the end

therefore,

total sum of mass initially = electron + proton + neutron

Total sum of mass finally = electron + proton + neutron

This must add all up