1. Collision Theory
2. Reaction Rates
3. Rate Laws
4. Reaction Mechanisms
5. Entropy [Reference]
6. Entropy Calculations
7. Spontaneous Reactions [Practice Diagrams ] [Practice Driving Forces]
8. Free Energy [Reference]
9. Free Energy Calculations
10. Reversible Reactions
11. Equilibrium Constants
12. Le Chatelier's Principle

Chapter 16

16-1 Collision Theory

- Reaction rates depend on the number of collisions and the energy that the collisions contain.

- Most reactions require an activation energy to provide energy for collisions.

- An activated complex exists right before two particles react. For an instant, the two particles are one before they break off into different particles. AB + CD ------> ABCD         > AD + CB. ABCD is the activated complex in this example.

16-2 Reaction Rates

- Higher temperatures make particles move faster, making collisions happen sooner. This will make a reaction go faster.

- Higher concentrations will make collisions happen sooner, making a reaction go faster.

- Smaller particle sizes (and therefore larger surface areas) increase collision frequency as well, making reactions go faster.

- Catalysts can lower activation energy requirements, speeding reactions.

16-3 Rate Laws

- The rate at which the reactant gets used up is proportional to that reactant's molarity.

16-4 Reaction Mechanisms

- Some reactions actually have multiple steps:

 S2O                > S2 + O

 S2O + O         > S2 + O2_

 2S2O              > 2S2 + O2

 Here O is a catalyst.

16-5 Entropy [ Reference]

- Entropy = disorder.

- Law of Disorder: things move spontaneously in the direction of chaos and disorder.

16-6 Entropy Calculations

- S = entropy J/K. DS = change in entropy J/K-mol.

- See Chempire's Online Standard Entropies Chart.

16-7 Spontaneous Reactions [Practice Diagrams] [Practice Driving Forces ]

- +DS promotes reaction spontaneity.

- -DH promotes reaction spontaneity.

- If both are positive or both are negative, you must determine which one takes precedence using DG (below).

16-8 Free Energy

- Free energy is a combination of entropy and enthalpy.

- Negative free energies are favorable to reaction spontaneity.

16-9 Free Energy Calculations [ Reference]

- DG = DH - TD S (T in Kelvins).

- See Chempire's Online Standard Enthalpies Chart.

- See Chempire's Online Standard Entropies Chart.

- See Chempire's Online Standard Free Energies Chart

16-10 Reversible Reactions

- Reactions can happen backwards too.

- Chemical equilibrium: normal and reverse reaction rates are equal.

- Equilibrium position: Equilibrium doesn't mean that there are equal amounts of reactants and products. The equilibrium probably favors one or the other.

16-11 Equilibrium Constants

- [square brackets] mean molarity.

- K(eq):

 K(eq) =    [product 1]^(coefficient of product 1) x [product 2]^(coefficient of product 2)_ 
                 [reactant 1]^(coefficient of reactant 1) x [reactant 2]^(coefficient of reactant 2)

16-12 Le Chatelier's Principle

- Equilibriums respond to strees by adjusting equilibrium position.

- Increasing concentration on one side of the equation will shift the equilibrium in favor of the other side.

- Increasing heat will shift the equilibrium in favor of the side that absorbs it.

- In a gaseous reaction, adding pressure will shift the equilibrium in favor of the side with the least number of moles of gas.

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