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# Thermodynamics - PowerPoint PPT Presentation

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).

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### Thermodynamics

By Alex Weber and Lee Cheung

• 25 C°, and 1 barr = 100kPa ≈ 1 atm

• 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)

• 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

• 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

• ΔHrxn = ΣHf products - ΣHf reactants

• -ΔH = exothermic

• +ΔH = endothermic

• Units (J/g or J/mol)

• 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

• Mmetal cΔT = mwater cΔT

• Mmetal c(Tf-Ti) = mwater c(Tf-Ti)

• q reaction = - (q water + q bomb)

• 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

• 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

• ∆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˚ < 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)

• Considering T= ΔH/ΔS when

• ΔS < 0 ΔS > 0

• ΔH < 0 Spontaneous at Always

• Low Temps Spontaneous

• ΔH > 0 Never Spontaneous

• Spontaneous at Higher Temps