Thermodynamics By Alex Weber and Lee Cheung

Standard Thermodynamic Conditions 25 C°, and 1 barr = 100kPa ≈ 1 atm

Specific Heat (C)  Energy required to raise a gram of material by 1° C C is a constant based on material and state of the 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 in grams Units for q in Joules +q means heat is transferred to the system -q means heat is transferred from the 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)  ΔH is the heat transferred into a system per mole or per gram ΔH = q/m= change in potential energy from products to reactants ΔH rxn = ΣH f products - ΣH f reactants -ΔH = exothermic +ΔH = endothermic Units (J/g or J/mol)

Hess’s Law If a reaction equals the sum of a series of reactions, then the overall ΔH equals the sum of ΔH from each individual 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)  ΔS is the 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  Mmetal c(Tf-Ti) = mwater c(Tf-Ti)  q reaction = - (q water + q bomb)

Changes in 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

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

Gibbs Free Energy Cont. ∆G = ∆G˚ + RT lnQ ∆G˚ = -RT lnK (at equilibrium), where R=8.314 J/(mol*K) and T = Temperature (K) K = Thermodynamic Equilibrium Constant Q= reaction quotient = K (at equilibrium) When ∆G˚ 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)

Spontaneity Considering T= ΔH/ΔS when ΔS 0 ΔH < 0 Spontaneous at Always Low Temps Spontaneous ΔH > 0 Never Spontaneous Spontaneous at Higher Temps