Thermochemistry Flashcards
Closed System
Exchange energy, but not matter
Isolated System
Nothing exchanged
Open System
Allows for exchange of energy and matter
Isobaric
Constant Pressure
Isothermal
Constant temperature (system must gain or lose energy to maintain)
Isochoric
Constant Volume, no net pressure-volume work
Adiabatic Process
No heat transferred to or from the system by surroundings
Heat
Transferrable Energy
q = mcΔt when there is no phase changes
Exothermic Reaction
Net release of energy into surroundings (-)
Endothermic Reaction
Net absorption of energy from surroundings (+)
Enthalpy
Total heat content of a system at a constant pressure (ΔH)
Hess’s Law
Enthalpy change of an overall reaction is equal to the sum of the standard heats of formation of the products minus the sum of the standard heats of formation of the reactants
ΔH = ΔH(prod) - ΔH(reac)
Entropy
ΔS = q(rev)/ T
Entropy increases during spontaneous reactions
Gibbs Free Energy
Energy available in system to do work (ΔG)
Gibbs Helmholtz Equation
ΔG = ΔH - TΔS ΔG = ΔG0 + RT ln Q
When will a reaction be spontaneous?
ΔG < 0
What happens if ΔG is zero?
ΔG = TΔS
What are the only temperature dependent states?
When both ΔH and ΔS have the same sign
What happens when ΔH is positive, but ΔS is negative?
The reaction is nonspontaneous at all temperatures
What happens when ΔS is positive and ΔH is negative?
The reaction is spontaneous at all temperatures
If both ΔH and ΔS are positive?
The reaction is spontaneous only at high temperatures
What does the rate of a reaction depend on?
The activation energy, no ΔG
Reaction Quotent
ΔG0 = -RT ln K(eq)
State Function
Depends only on the initial and final states of a system, not the path
Standard Free Energy (ΔG0)
ΔG calculated at 1 atm and 0 K
