Thermodynamics Flashcards
Heat
Thermal kinetic energy from the random motion of particles
Exothermic
Heat goes from the system to the surroundings; heat is “released” (-)
Endothermic
Heat goes from surroundings to system; heat is “absorbed” (+)
Spontaneity
Whether or not a process occurs under a given set of conditions without a driving force
Entropy
Energy dispersion disorder (number of microstates).
The second law of Thermodynamics
For a process to be spontaneous entropy in the universe must increase
What is the entropy order for s, l, and g
(s)<(l)«<(g)
What causes entropy to increase
- Increase in temperature, higher the molecular complexity
- Increase in molar mass, the more something can move around
- Increase in moles of gas, and the higher the number of particles
- Increase in randomness of molecules; such as formation of a gas
- Condensation (formation of solid) decreases entropy
- Dissolution increases entropy
Spontaneous
Occurs as written
What are the rules to determine entropy in aqueous solutions
The smaller the charge of the solute, the more entropy increases
Why do smaller charges cause entropy to increase
Higher charged ions cause more order in the solution so the entropy decreases
How do you calculate entropy
Δ S rxn = ΔS (products) - ΔS (reactants)
Third Law of Thermodynamics
For a pure crystalline substance at absolute zero (0 K), entropy equals 0
How do you get the Δ S surroundings/entropy for a phase change?
ΔS = - ΔH/temp
Gibbs free energy
Energy available to do something or energy needed to do something (in kj/mol)
What does it mean if G is (+/-)
-G: spontaneous
+G: nonspontaneous
How to determine G when given the values?
ΔG = G (products) - G ( reactants)
G formula
ΔGrxn = ΔHrxn - T * Srxn
How do you determine ΔG if you are given observations?
(+) - (-) = always (-) (-) - (+) = always (+) (+) - (+) = depends; as T rises, G becomes negative (-) - (-) = depends; as T rises, G becomes positive
Gibbs free energy formula without standard G
ΔG = -RTln(K)
How to get quotient K/Q?
[reactants]
(only gas or aqueous included)
Equilibrium rules
Q = K: at equilibrium
Q > K: too many products; reaction must proceed in reverse
Q < K: too few products; reaction must go forward
How do you get the entropy of the universe?
ΔS universe = ΔS system + ΔS surroundings
How do you get the boiling/melting point?
T = ΔHrxn / ΔSrxn
How can you get heat given ΔH rxn?
Heat = moles x ΔHrxn / mole
How do you get ΔS sub?
ΔS sub = ΔH sub * moles of element
