1. AP Chemistry Zumdahl Notes, 9th ed.
A Brief Collection of notes, Chapter 6
Feel free to open these files and annotate as you feel the need…this is
for your success.

2. Thermochemistry: the Nature of Energy
Energy: the capacity to do work or to produce heat
Law of Conservation of Energy: energy can be converted from one form to another but can be neither created nor destroyed
Potential energy: due to position or composition (chem. Bonds)
Kinetic energy: due to the motion of the object; KE = ½ mv2
Temperature: a measure of the avg. KE of something
Heat: the transfer of energy, involving a change in temperature (measurable!)
Work: force applied over a change in distance

3. Thermochemistry: the Nature of Energy, cont.
State function or property: a function or property dependent upon the state of the system at a specified time
Example: boiling point at a given altitude/location
Energy is a state function, but heat or work are not

4. Thermochemistry: the Nature of Energy: chemical Energy
System: that which we are focused on
Surrounding: everything around the system
Exothermic: energy flows out of the system
Endothermic: energy flows into the system
Reality: energy flowing in/out must equal put in/out…energy is conserved!
Thermodynamics: the study of energy and its movement
First law: the energy of the universe is constant
ΔE = q + w change in energy = heat and work done
If ΔE<0, exothermic; if ΔE>0, endothermic
Almost always, if not specified, take view of system, not surroundings!
May have changes in energy, work, or both, so pay attention to details!
w= -PΔv; p always refers to external pressure, that causing a compression/resists an expansion

5. Thermochemistry: enthalpy and calorimetry
Enthalpy: a state function, whose symbol is H, means the sum of the internal energy of a system and the product of pressure and volume
H = E + PV
Caveat: at constant pressure, H = q
ΔH = Hproducts –Hreactants
ΔH = ΔE + PΔV
Calorimetry: the science/study of measuring heat
Heat capacity: C= heat absorbed/increase in temperature
Specific heat capacity: J/g°C or J/gK
Could be molar, so J/°C or J/K
Typically done as constant pressure (atmospheric) so no work done!
Q = smΔT s is specific heat, m is mass…if delta T (+), q (+), endothermic!
If done as constant volume, still no work done!

6. Thermochemistry: Hess’s Law
Hess’s Law: the total enthalpy change of a reaction is the sum of the enthalpy changes for the steps which can make up the overall reaction; this means that you can solve for either the total enthalpy change or that of a single step, providing you have the data for the other steps
Characteristics of enthalpy changes
If a reaction is reversed, the sign of ΔH is also reversed
The magnitude of ΔH is directly proportional to the quantities of reactants and products in a reaction; if the coefficients in a balanced reaction are multiplied by an integer, the value of ΔH is multiplied by the same integer

7. Thermochemistry: Std. enthalpies of formation
Std. enthalpy of formation: the change in enthalpy that arises from the formation of one mole of a given compound from its componenet elements in their standard states; ΔH°
Conventions for compounds:
The std. state of a gaseous substance is that pressure = 1 atm
For a pure substance that is a liquid or solid, that is its std state
For a substance present in a solution, the std state is 1. molar
Conventions for elements:
The std state of an element is the form at has at 1 atm and 25°C
ΔH°reaction = Σ npΔH°(products) – Σ nrΔH°(reactants) (n is moles)

8. Thermochemistry: enthalpy calculations