Flashcards in Thermochemistry Deck (25):
Exchange energy, but not matter
Allows for exchange of energy and matter
Constant temperature (system must gain or lose energy to maintain)
Constant Volume, no net pressure-volume work
No heat transferred to or from the system by surroundings
q = mcΔt when there is no phase changes
Net release of energy into surroundings (-)
Net absorption of energy from surroundings (+)
Total heat content of a system at a constant pressure (ΔH)
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)
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
ΔG0 = -RT ln K(eq)
Depends only on the initial and final states of a system, not the path