1. Entropy and Free Energy Thermochemistry
Chapter 18, section 4
Chapter 17

2. Free energy Energy available to do work
Not usually used efficiently…internal combustion engine is 30% efficient.
Spontaneous reaction: occurs naturally and favors the formation of the products at specific conditions.
Produces substantial amounts of products at equilibrium and releases free energy (Fireworks).
Nonspontaneous reaction: does not favor the formation of products at the specific conditions.
In nearly all reversible reactions, one reaction is favored over the other.
Some reactions that are nonspontaneous at one set of conditions may be spontaneous at other conditions.
Changing temperature/pressure or coupled with spontaneous reaction.

3. Entropy Measure of the disorder of a system
Law of disorder: natural tendency is for systems to move in the direction of maximum disorder or randomness.
An increase in entropy favors spontaneous reactions whereas as decrease in entropy favors a nonspontaneous reaction.
Figure on page 570

4. Thermochemistry
Study of energy changes that occur during a chemical reactions and changes in state.
Potential energy: stored energy (gasoline)
Kinetic energy: energy of motion
Heat (q) is energy that transfers from one object to another because of temperature differences between them.
Heat always flows from warmer object to cooler object.
Heat is measured in calorie and joule
calorie (cal) is the quantity of heat required to raise temperature of 1 g pure water 1 degree Celcius.
Dietary calorie = 1 kcal = 1000 cal

5. Conservation of energy
In any chemical or physical change, energy is neither created nor destroyed.
Endothermic reaction: system gains heat and the surroundings cool down
Exothermic reaction: system releases heat and the surroundings heat up

6. Enthalpy Enthalpy (∆H) = heat (q)
In every chemical reaction, heat is either released or absorbed and entropy either increases or decreases.
The size and direction of enthalpy and entropy changes determine whether a reaction is spontaneous
Exothermic + increase in entropy = spontaneous
Endothermic + decrease in entropy = nonspontaneous
Table 18.3 on page 571
Figure 18,25 on page 572

7. Gibbs Free Energy All spontaneous reactions release free energy.
Some of this energy becomes available to do work which is called Gibbs Free Energy.
The numerical value of a ∆G is negative in spontaneous reactions because the system loses free energy.

8. Heat capacity
Depends on both an objects mass and chemical composition.
Specific heat of a substance is the amount of heat it takes to raise the temperature of 1 g of the substance 1 degree Celsius.

9. Calorimetry Precise measurement of heat flow into or out of a system.
In calorimetry, the heat release by the system is equal to the heat absorbed by its surroundings. Conversely, the heat absorbed by the system is equal to the heat released by its surroundings.
Figure 17.5 on page 511