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## PowerPoint Slideshow about ' Thermodynamics' - kiaria

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### 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
- ΔHrxn = ΣHf products - ΣHf 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˚ < 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)

Spontaneity

- 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

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