CHEM 142 Lecture Notes - Lecture 1: Intermolecular Force, Chemical Potential, Spontaneous Process
Spontaneous process -- one that occurs without outside intervention (if 2 things are combined a
reaction will occur without outside help)
--the reverse reaction will always be nonspontaneous and require continuous outside influence
Eg. Boulder on top of a hill going down = spontaneous. However, a boulder needs to be pushed up a hill
Work (w) -- force acting over a distance
Heat (q) -- flow of E caused by a difference in T
Energy -- something an object possesses
Work and heat -- ways objects exchange energy
KE - motion
PE - due to position/composition
1st law of thermodynamics -- energy can change forms but can't be created or destroyed
Delta H = enthalpy of rxn
--quantifies thermal energy transfer in/out of a system
Exothermic -- rxn proceeds from higher to lower PE and heat is emitted (delta H < 0)
Endothermic -- lower to higher PE -- requires an input of energy (heat) -- delta H > 0
Delta H = sum of delta H of bonds broken + sum of delta H of bonds formed
The transfer of heat from a substance of higher to lower T results in greater E dispersal
Entropy (S) -- spreading out of E
--increases when matter changes from solid to liquid or gas
--- solids -- molecules/atoms are close together -- E is less spread out
2nd law -- criterion for spontaneity is an increase in S
As long as delta S(universe) > -delta S(system) then a reaction can occur
Eg. Freezing of ice:
(increase in intermolecular forces -> decrease in PE -> E is released to surroundings)
Exothermic rxns are often more favorable -- they release E to surroundings
At constant P -- quantity of heat(q) = delta H(sys):
--exothermic rxns have a tendency to be spontaneous at low T but less so at higher T
Gibbs free E (G) -- sometimes called chemical potential
Delta G = delta H(sys) - T*delta S(sys)
Positive -- nonspontaneous
Negative -- spontaneous
0 = equilm
Lecture 1/class 3
January 23, 2018
1:12 PM
class notes Page 1
Document Summary
Spontaneous process -- one that occurs without outside intervention (if 2 things are combined a reaction will occur without outside help) -the reverse reaction will always be nonspontaneous and require continuous outside influence. Boulder on top of a hill going down = spontaneous. However, a boulder needs to be pushed up a hill. Work (w) -- force acting over a distance. Heat (q) -- flow of e caused by a difference in t. Work and heat -- ways objects exchange energy. 1st law of thermodynamics -- energy can change forms but can"t be created or destroyed. -quantifies thermal energy transfer in/out of a system. Exothermic -- rxn proceeds from higher to lower pe and heat is emitted (delta h < 0) Endothermic -- lower to higher pe -- requires an input of energy (heat) -- delta h > 0. Delta h = sum of delta h of bonds broken + sum of delta h of bonds formed.
