Thermodynamics Flashcards
Extensive properties
Proportional to size of system
ex. volume, # of moles
Intensive properties
Independent of size of system
ex. pressure and temperature
Temperature
Amount of molecular movement of a substance, proportional to translational KE
KE (avg/molecule) = 3/2 kT k=1.38x10^-23 J/K
KE (avg/mole) = 3/2 RT
Kelvin
°C + 273
State Functions
Properties that describe the current system state (pathway independent)
ex. internal nrg, temp, pressure, volume, enthalpy, gibbs nrg, entropy
Internal Energy: KE and PE types
KE: vibrational, rotational, translational
PE: electronic, intermolecular, rest mass nrg
Heat and types of
Due to random collisons betweeen molecules of two systems
Conduction: physical contact
Convection: transfer via fluid
Radiation: via electromagnetic waves
Work
Any energy transfer that isn’t heat
W=-PΔT P=F/A
1st law of thermodynamics
Total energy of a system and surroundings is always conserved
ΔE=q+w
Energy out of system ΔE is -
Energy into system ΔE is +
Enthalpy (H)
ΔH=ΔU+PΔV (constant pressure) in J
Standard Enthalpy of Formation ΔHf
The ΔH needed to create 1 mole of the compound from raw elements in standard state.
ΔH°rxn=ΔHf°prod - ΔH°reactants
ΔH + : endothermic
ΔH - : exothermic
Entropy (S)
Nature’s tendency to make most probable arrangement
0
Gibbs free energy
ΔG=ΔH-TΔS
-ΔG = spontaneous
ΔH | ΔS | ΔG=ΔH-TΔS
- | + | - Always spontaneous
- | - | - or + Spontaneous at low T, not at high T
+ | + | + or - Spontaneous at high T, not at low T
+ | - | + Never spontaneous
Hess’ Law
Sum of enthalpy changes for each step equals total enthalpy charge
Equilibrium constant [K]
K=[C]^c [D]^d / [A]^a [B]^b = prod^coeff/reactants^coeff
don’t include solids!
