THERMOCHEMISTRY & THERMODYNAMIC
ENERGY
ΔE = E(f) - E(i)
ΔE = q + w
lose energy = E(f) < E(i)
gain energy = E(f) > E(i)
q = (+) : system gain heat
q = (-) : system loses energy
w = (+) : work done on system
w = (-) : work done by system
ΔE(universe) = ΔE(system) + ΔE(surrounding) = 0J
ENTHALPY
ΔH = ΔE + PΔV
ΔH = q if work done by system w=-PΔV
ΔH = H(f) - H(i)
ΔH = mcΔT
CALORIMETRY
A Coffee Cup Calorimeter
-q(solid) = q(water)
Bomb Calorimeter
-q(sample) = q(calorimeter)
q = cΔT
Stoichiometry of Thermochemical Equation
2 aspects of enthalphy change
sign = sign of a forward reaction is opposite that of the reverse reaction
magnitude = magnitude of ΔH is proportional to the amount of substance in the reaction
Hess Law
the difference between the H of the reactant and the product has the same value even through the reaction take place differently
Hess Law Summation
ΔH = ΣmΔH(f)products - ΣnΔH(i)reactants
Spontaneous Process
chemical or physical change occurs by itsef
Entrophy,S
a measure of randomness or disorder of a system
randomness of solid <liquid <gas
ΔS = S(f) -S(i)
ΔS>0,implies the system more disordered
ΔS<0,implies the system less disordered
molecular interpretation of S
have to consider the no. of molecule of gas in balanced equation and the state of matter
ΔS = q / T (equilibrium process)
2nd Law of Thermodynamics
ΔS = ΣmΔS(f)products - ΣnΔS(i)reactants
total energy of a system and its surrounding always increases for a spontaneous process
ΔS = entropy created - q/T
Gibbs Free Energy
predict whether a given reaction will be spontaneous
ΔG = '+', non-spontaneous, less product
ΔG = ΔH - TΔS
ΔG = '-', spontaneous, more product
ΔG = ΣmΔG(f)products - ΣnΔG(i)reactants
ΔG = ΔG + RT ln Q
equilibrium constant, Kc = [G]^g[H]^h / [A]^a[B]^b