Thermodynamics

- Enthalpy (∆H) AND Entropy(∆S) are state functions (only numbers that matter are beginning and end)

- Enthalpy: measure of the TOTAL ENERGY of the system (joules)

Bond Formed = -∆H (energy released)

Bond BROKEN = +∆H (energy absorbed)

- Hess’s Law: summation of enthalpies

- Spontaneity depends on ∆G (∆G = ∆H - T∆S) graphable

∆G will tell you whether a reactions happens or not!

…will tell you NOTHING about rxn rate.

∆G / spontaneity is dependent on temperature, NOT necessarily on ∆H and ∆S.

NEG ∆G = spontaneous

POS ∆G = non spontaneous

ZERO ∆G = equilibrium

∆Gf indicates whether we have a stable or unstable compound relative to its elements.

NEG ∆Gf = STABLE… will spontaneously form compound.

POS ∆Gf = UNSTABLE… will not spon. form compound, need to input energy into the system

POS ∆S = increase in disorder

NEG ∆S = decrease in disorder

Consider why according to eq:

ex: ATP-coupled reactions

ex2: Hydrogen bonding

Apr 09, 2011

Which of the following best describes enthalpy?

(a) Energy that is not available for work in a thermodynamic system (Entropy)
(b) Energy stored in a system derived from its configuration (PE)
(c) The energy of motion in an object (KE)
(d) The total energy of a thermodynamic process (Enthalpy)