Thermodynamics

Thermodynamics

Definitions

Equations

Useful Facts

Images

Reaction Profiles

Maxwell-Boltzmann Distribution and how Temperature interacts with Activation Energy

Phase Changes in Water

Definitions

Net Reaction Equation = the overall equation for a multistep reaction pathway. Add up the left and right sides, and cancel out anything that appears on both sides.

Transition State = a transient, theoretical arrangement of atoms that is very high energy, and is the “transition” between the arrangement of bonds in the reactants and the arrangement of bonds in the products.

Catalyst = a molecule that is not consumed in the process, but speeds it up by stabilizing the transition state and thus reducing the Activation Energy (Ea). Does not appear in the net reaction equation.

Intermediate = a molecule that is formed “in the middle” of a multi-step reaction pathway, and consumed before it is over. Does not appear in the net reaction equation.

Temperature  = average KE of the molecules in the system.

Enthalpy  = Total Energy of the Molecules in the system

Enthalpy  = KEmolecules in the system + Bond Energiesmolecules in the system

Heat = ∆ Enthalpy

Entropy = Disorder of the system = “Elbow Room” given to the molecules in the system

Equilibrium = the state of the chemical system when there is no more free energy to drive the reaction in either direction. The [Products] and [Reactants] stays the same over time.

Reaction Quotient (Q) = current ratio of

Equilibrium Expression (Keq) = ratio ofat Equilbrium. Not necessarily equal to 1.If >>1, products are thermodynamically favored. If <<1, reactants are thermodynamically favored.

STP = Standard Temperature & Pressure : 0oC & 1 atm

Standard Conditions : 25oC & 1 atm & Q = 1

Equations

∆ U = Q - Wby the system [U = internal energy of the system, Q = Heat, W = Work] [1st Law of Thermodynamics]

Suniverse = Ssystem + Ssurroundings [S = Entropy]

∆ Suniverse ≥ 0 [for all processes. If ∆ Suniverse = 0, the process is reversible]

∆ G = ∆ H - T∆S

∆ Go = ∆ Ho - T∆So  [Same as above, but only for standard conditions]

∆ G = RT ln (Q/Keq)

∆ Go  = -RT ln Keq

Useful Facts

- At STP, one mole of ideal gas occupies 22.4L

- Over time, a system not at equilibrium will proceed in the direction that makes Q = Keq. If Q>Keq, the products will be turned into reactants (i.e.: the reaction will be driven to the left), and vice versa. [Le Chatelier’s Principle]

- The side of the reaction with more moles of gas is Entropically favored.

- If the reaction proceeds in a single step, the exponents for the reactants in the equilibrium expression are those in the rate law.

- Only gases and dissolved species can change their concentration. (Solids and liquids are incompressible). Therefore, only gases and aqueous species are put into the Keq.


Images

Reaction Profiles

Reaction Profile:

sn2profile.gif

Reaction Profile with a Catalyst:

catprofile.gif


Reaction Profile where there is an Intermediate:

sn1profile.gif


Maxwell-Boltzmann Distribution and how Temperature interacts with Activation Energy

mxspd.gif

mbdistrib2.gif

maxboltz2.gif

Phase Changes in Water

Graph showing specific heat (slope of the diagonal parts), Heat of Fusion (Lower flat part) and Heat of Vaporization (Upper Flat Part):

specific-latent-graph.png

For more Detail about Heating Curves, see the section in the page on Phase Equilibria.