Thermochemistry Flashcards
Define isolated, closed, and open systems
Isolated: No matter or energy exchanged with surroundings
Closed: No matter, only energy exchanged with surroundings
Open: Matter and energy exchanged with surroundings
Define spontaneous and non-spontaneous processes
Spontaneous can occur without being driven by energy from outside source (not including activation E)
Change in internal energy U of a system
∆U = Q - W (Work done BY the system)
Define endo and exothermic process
Endo = +Q Exo = -Q
Heat absorbed in a process
Q = mc∆T (c = specific heat)
How to calculate standard enthalpy of formation
Enthalpy change from forming one mole of substance from elements in their standard states
Standard heat of reaction
Enthalpy change if reaction carried out in standard conditions. Determined by difference in standard heat of formation of products and reactants
∆H = ∑∆Hº products - ∑∆Hº reactants)
Hess’s law
Heats of reactions, entropy, Gibbs free energy (state functions) are additive
How to calculate ∆H rxn from bond dissociation energies?
∆Hrxn = ∑∆H bonds broken + ∑∆H bonds formed (energy in - energy out)
What’s the second law of thermodynamics?
Energy spontaneously disperses from being localized to spread out if not hindered from doing so
∆S=
Q.rev / T
Change in Gibbs free energy
∆G = ∆H - T∆S
What is the change in Gibbs free energy?
Max E released by process (at constant T and P) available to perform work. Indicates spontaneous vs non-spontaneous
When is ∆G temp dependent?
When ∆S and ∆H have the same sign
Compare kinetic control vs thermodynamic control
The reaction with the lowest E.a will proceed fastest, but given enough time and assuming a reversible rxn, the thermodynamically favored reaction will proceed until the rxn reaches equilibrium.
