CHEM 1B Lecture 10: Lecture 10 Thermodynamics
Document Summary
Spontaneous process leads to state that is statistically more probable: Predicting entropy and entropy changes for chemical rxns. Enthalpy changes: hr = nphf (products) - nrhf (reactants) Reference point for enthalpy: elements in their standard state. Entropy changes: sr = nps (products) - nrs (reactants) (absolute value) S = standard molar entropy jk-1 mol-1 at t. Standard molar entropies and 3rd law of thermodynamics - the entropy of a perfect crystal at absolute zero is zero. A state of perfect order will have zero entropy. Standard molar entropies are tabulated with s = c ln (tf/ti) Also they are different depending the states of the substances. More massive atoms have more closely spaces energy levels: more microstates = higher entropy. The different structures give the same elements different entropy levels. Diamond and graphite both forms of carbon, but diamond has higher entropy than graphite. Molecules have more degrees of freedom than atoms.
