Thermodynamics
Standard thermodynamic conditions
25 C°, and 1 barr = 100kPa ≈ 1 atm
Heat Transferred
 Specific Heat (C) - Energy required to raise a gram of material by 1° C
Constant based on material and state of matter
Units in J/g° C
C = 4.18 J/g° C (For Water)
 Heat Transferred (q)
q= mC(ΔT) where C is specific heat, ΔT is the change in temperature (in ° C), and
m is mass of matter in grams
Units for q in J
+q means heat transferred to system, -q means heat is transferred from system
Bond Energies
 q = Σ Reactants Bond Energy – Σ Products Bond Energy (note: reactants –
products)
Endothermic reactions need heat/energy added to progress
Breaking bonds requires heat/energy to progress
Exothermic reactions give off heat/energy during the reaction
Forming bonds gives off heat/energy
Potential energy in an elemental state = 0
Enthalpy
 (ΔH) – Heat transferred into a system per mole or per gram
ΔH = q/m= change in potential energy from products to reactants
ΔHrxn = ΣHf products - ΣHf reactants
-ΔH = exothermic
+ΔH = endothermic
Units (J/g or J/mol)
 Hess’s Law
If a reaction = the sum of a series of reactions, then the overall ΔH = the sum of
ΔH from each reaction
Reverse reactions = reverse signs
If you change the coefficients of a reaction by a certain factor, then change ΔH by
the same factor
Entropy
 ΔS = measure of randomness of molecules
ΔS = the change in S from products to reactants
Gases are the most random and have the highest entropy, solids the lowest
Product favored reactions have higher entropy
Units of J/K*mol
Calorimetry
 Mmetal cΔT = mwater cΔT
Mmetalc (Tf-Ti) = mwater c(Tf-Ti)
q reaction = - (q water + q bomb)
Changes of State
 q=mHf or q=mHv (Hf = Heat of fusion, Hv = Heat of vaporization)
Heat of fusion = heat required to melt a substance into liquid
Heat of vaporization = heat required to vaporize substance into gas
Spontaneity
 Gibbs Free Energy
ΔG = ΔH - TΔS (T is in K)
When ΔG is negative reaction is spontaneous and vice versa
Threshold Energy = when ΔG = 0, equation is at equilibrium
Spontaneous reactions favor products
Considering T= ΔH/ΔS when
ΔS < 0
ΔS > 0
ΔH < 0
ΔH > 0
Spontaneous at
Low Temps
Always
Spontaneous
Never
Spontaneous
Spontaneous
at Higher Temps
∆G = ∆G˚ + RT lnQ
∆G˚ = -RT lnK (at equilibrium)
R=8.314 J/(mol*K)
K = Thermodynamic Equilibrium Constant
T = Temperature (K)
Q= reaction quotient = K (at equilibrium)
When ∆G˚ < 0 and K > 1 Reaction is product favored (spontaneous)
When ∆G˚ = 0 and K = 1 Reaction is at equilibrium
When ∆G˚ > 0 and K < 1 Reaction is reactant favored (non-spontaneous)