Entropy, S, is the tendency towards randomness or disorder in a system

Can We Write Your Essay?

Ace your next assignment with help from a professional writer. Free proofreading and copy-editing included.

– an ordered arrangement of particles has a lower entropy/disorder than the same number of particles in random arrangements

Entropy becomes more disordered with:

1.) ^ Temperature – more chaotic motion

2.) ^ Volume of gases

3.) change in phys. State

A change in entropy is calculated by subtracting the entropy of the reactants from the entropy of the products

DS = Sproducts – Sreactants

If DS>0, Sproducts > Sreactants and DS has increased (+)

If DS<0, Sproducts < Sreactants and DS has decreased (-)

Physical Changes where an increase in S is found:

– change in state (s>l, s>g, l>g) or dissolving

– water falling (i.e. rain)

– solutes moving from high to low conc. until equil. is met

Chemical Changes where is increase in S is found:

– more moles of products than reactants

– complex molecule broken into simpler ones

– change of state due to chemical change

Spontaneous Reactions

-spontaneous rxns are always accompanied by an increase in S

– exothermic rxns are spontaneous at all T and have an increase in S

– endothermic rxns will only be spontaneous if there is an increase in S

Second Law of Thermodynamics: All changes, either directly or indirectly, increases the entropy of the universe. Mathematically, this means

DSuniverse = DSsystem + DSsurroundings

The system can decrease its entropy as long as there’s a larger increase in entropy of the surroundings

READ:
What are acid/ base Indicators?

Predicting Spontaneity

Gibbs Free Energy: energy available to do work

Reactions/changes are spontaneous (occur with no input of outside E) if accompanied by a decrease of Gibbs Free Energy

DG must be LESS THAN 0 (negative value) for a reaction to be spontaneous.

A rxn must release free energy to be spontaneous. (lose free energy, lose the ability to do work)

DG = DH – TDS         Called the Gibbs-Helmholtz free energy equation

When DG is -, forward rxn is favourable

When DG is +, reverse rxn is favourable

When DG is 0, the rxn is at equil.

Exothermic reactions are favourable because DH is –

Most rxns are more favourable at higher T, as this increases the value of

-TDS, this makes DG –

DHDS-TDSComment
+DH and -TDS are (-) therefore DG = – therefore spont.
++DH +, -TDS + therefore DG = + therefore non. spont
+DH – and -TDS + therefore DG = – or +

– if T is low than DG = –

++DH + and -TDS is – therefore DG = – or +

– if T is high than DG = –

Equilibrium occurs in a system when it has reached its maximum entropy.  A maximum state of disorder has been reached.

Can We Help with Your Assignment?

Let us do your homework! Expert writers in all subject areas are available and will meet your assignment deadline.

guest
0 Comments
Inline Feedbacks
View all comments