AP* Chemistry (modified from NMSI resources by René McCormick)
Thermochemistry & Thermodynamics
First Rule of Chem Club:
Breaking bonds REQUIRES energy
Bonds forming RELEASES energy
Breaking bonds & attractive forces (IMFs) is always ENDOTHERMIC.
• Break bond = take atoms in a molecule that are already connected (& stable) and separate them
into individual atoms (& much less stable)
Allowing bonds to be made & attractions to occur is always EXOTHERMIC.
• Make bond = take unstable, individual atoms and allow them to attract and bond to other atoms to
make a more stable molecule
Key terms:
Energy (E): the ability to do work or produce heat; the sum of all potential and kinetic energy in a system is
known as the internal energy of the system
Potential energy: in chemistry this is usually the energy stored in bonds (in a reaction there are differences
in the attractive forces within the reactants and the products)
Kinetic energy: energy of motion, usually of particles, proportional to Kelvin temperature; kinetic energy
depends on the mass and the velocity of the object: KE = ½ mv2
Law of Conservation of Energy: energy never created nor destroyed (First Law of Thermodynamics)
Heat (q): transfer of energy in a process; flows from a warmer object to a cooler one; heat transfers because of
temperature difference
Temperature (T): measure of the average kinetic energy of the particles in a substance; measured in Celsius or
Kelvin (Kelvin used for calculations, graphs, etc.)
Enthalpy (H): heat content at constant pressure
Enthalpy of reaction (ΔH rxn ): heat exchanged by a chemical reaction
Enthalpy of formation (ΔH f ): heat exchanged when ONE mole of compound is formed from elements in
their standard states
Enthalpy of fusion (ΔH fus ): heat absorbed to melt 1 mole of solid to liquid at the melting point
Enthalpy of vaporization (ΔH vap ): heat absorbed to change 1 mole liquid to gas at the boiling point
System: area of the universe we are focusing on (i.e., the experiment)
Surroundings: everything outside of the system
Endothermic: net absorption of energy (heat) by the system; energy is a reactant
Exothermic: net release of energy (heat) by the system; energy is a product
Entropy (S): measure of disorder in the system
Gibb’s Free Energy (G): criteria for sponteneity and amount of free energy to do work
Work (w): force acting over distance (w = F x d; for gases, w = –PΔV)
Standard Conditions: standard lab conditions = 1 atm of pressure, 25°C, and solutions are 1.0 M.
All of this information is communicated by adding the symbol ° to G, H or S.
AP* is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product.
Portions of this document are modified from NMSI AP Chemistry notes © 2008 by René McCormick.
, Potential Energy
Particles have potential energy because of attractive & repulsive forces between them.
“Coulombic attraction” = attraction or repulsion between charged particles (CB’s “favorite” term)
k q1 q2
Coulomb’s Law: F=
d2
F = force q = charge on particle
(different than q as heat)
k = Coulomb’s constant d = distance between particles
If charges have the same sign, the force is repulsive; opposite charges cause an attractive force.
Nuclei repel nuclei; electrons repel electrons; nuclei attract electrons (and vice versa).
Laws of Thermodynamics
• 0th Law of Thermodynamics: If two systems are in thermal equilibrium with a third system, then they are in
thermal equilibrium with each other.
• 1st Law of Thermodynamics: “Law of Conservation of Energy”
o The internal energy of a system may change as heat is transferred into or out of the system or work is done
on or by the system.
ΔE = q (heat) + w (work)
o ΔE because we can’t measure the total internal energy, but we can measure changes
o “q” tells us if the process in endothermic (+q, heat absorbed) or exothermic (–q, heat released)
Always in terms of the system
o “w” tells us if work is done on the system (+w) or by the system (–w)
w = F x d = –PΔV
+w = gas compressing; –w = gas expanding
Exercise 1
Calculate ∆E for a system undergoing an endothermic process in which 15.6 kJ of heat flows and where 1.4 kJ of
work is done on the system.
= 17.0 kJ
Exercise 2
Calculate the work associated with the expansion of a gas from 46 L to 64 L at a constant pressure of 15 atm.
= –270 L⋅atm
Exercise 3
A balloon is being inflated to its full extent by heating the air inside it. In the final stages of this process, the volume
of the balloon changes from 4.00 x 106 L to 4.50 x 106 L by the addition of 1.3 x 108 J of energy as heat. Assuming
that the balloon expands against a constant pressure of 1.0 atm, calculate ∆E for the process. (1 L ⋅ atm = 101.3 J.)
= 7.9 x 107 J
AP* is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product.
Portions of this document are modified from NMSI AP Chemistry notes © 2008 by René McCormick.
Thermochemistry & Thermodynamics
First Rule of Chem Club:
Breaking bonds REQUIRES energy
Bonds forming RELEASES energy
Breaking bonds & attractive forces (IMFs) is always ENDOTHERMIC.
• Break bond = take atoms in a molecule that are already connected (& stable) and separate them
into individual atoms (& much less stable)
Allowing bonds to be made & attractions to occur is always EXOTHERMIC.
• Make bond = take unstable, individual atoms and allow them to attract and bond to other atoms to
make a more stable molecule
Key terms:
Energy (E): the ability to do work or produce heat; the sum of all potential and kinetic energy in a system is
known as the internal energy of the system
Potential energy: in chemistry this is usually the energy stored in bonds (in a reaction there are differences
in the attractive forces within the reactants and the products)
Kinetic energy: energy of motion, usually of particles, proportional to Kelvin temperature; kinetic energy
depends on the mass and the velocity of the object: KE = ½ mv2
Law of Conservation of Energy: energy never created nor destroyed (First Law of Thermodynamics)
Heat (q): transfer of energy in a process; flows from a warmer object to a cooler one; heat transfers because of
temperature difference
Temperature (T): measure of the average kinetic energy of the particles in a substance; measured in Celsius or
Kelvin (Kelvin used for calculations, graphs, etc.)
Enthalpy (H): heat content at constant pressure
Enthalpy of reaction (ΔH rxn ): heat exchanged by a chemical reaction
Enthalpy of formation (ΔH f ): heat exchanged when ONE mole of compound is formed from elements in
their standard states
Enthalpy of fusion (ΔH fus ): heat absorbed to melt 1 mole of solid to liquid at the melting point
Enthalpy of vaporization (ΔH vap ): heat absorbed to change 1 mole liquid to gas at the boiling point
System: area of the universe we are focusing on (i.e., the experiment)
Surroundings: everything outside of the system
Endothermic: net absorption of energy (heat) by the system; energy is a reactant
Exothermic: net release of energy (heat) by the system; energy is a product
Entropy (S): measure of disorder in the system
Gibb’s Free Energy (G): criteria for sponteneity and amount of free energy to do work
Work (w): force acting over distance (w = F x d; for gases, w = –PΔV)
Standard Conditions: standard lab conditions = 1 atm of pressure, 25°C, and solutions are 1.0 M.
All of this information is communicated by adding the symbol ° to G, H or S.
AP* is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product.
Portions of this document are modified from NMSI AP Chemistry notes © 2008 by René McCormick.
, Potential Energy
Particles have potential energy because of attractive & repulsive forces between them.
“Coulombic attraction” = attraction or repulsion between charged particles (CB’s “favorite” term)
k q1 q2
Coulomb’s Law: F=
d2
F = force q = charge on particle
(different than q as heat)
k = Coulomb’s constant d = distance between particles
If charges have the same sign, the force is repulsive; opposite charges cause an attractive force.
Nuclei repel nuclei; electrons repel electrons; nuclei attract electrons (and vice versa).
Laws of Thermodynamics
• 0th Law of Thermodynamics: If two systems are in thermal equilibrium with a third system, then they are in
thermal equilibrium with each other.
• 1st Law of Thermodynamics: “Law of Conservation of Energy”
o The internal energy of a system may change as heat is transferred into or out of the system or work is done
on or by the system.
ΔE = q (heat) + w (work)
o ΔE because we can’t measure the total internal energy, but we can measure changes
o “q” tells us if the process in endothermic (+q, heat absorbed) or exothermic (–q, heat released)
Always in terms of the system
o “w” tells us if work is done on the system (+w) or by the system (–w)
w = F x d = –PΔV
+w = gas compressing; –w = gas expanding
Exercise 1
Calculate ∆E for a system undergoing an endothermic process in which 15.6 kJ of heat flows and where 1.4 kJ of
work is done on the system.
= 17.0 kJ
Exercise 2
Calculate the work associated with the expansion of a gas from 46 L to 64 L at a constant pressure of 15 atm.
= –270 L⋅atm
Exercise 3
A balloon is being inflated to its full extent by heating the air inside it. In the final stages of this process, the volume
of the balloon changes from 4.00 x 106 L to 4.50 x 106 L by the addition of 1.3 x 108 J of energy as heat. Assuming
that the balloon expands against a constant pressure of 1.0 atm, calculate ∆E for the process. (1 L ⋅ atm = 101.3 J.)
= 7.9 x 107 J
AP* is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product.
Portions of this document are modified from NMSI AP Chemistry notes © 2008 by René McCormick.
