Thermodynamics Chapter 19

Important vocabulary to review: Heat Temperature Energy State function/property System Surroundings Work Driving force

Internal Energy (E) E system = KE system + Pe system But total energy cannot be measured, only ΔE ΔE = E products - E reactants ΔE = q + w q (+) heat absorbed by system, endothermic q (-) heat released by system, exothermic w (+) work done on system PΔV (contracts) w (-) work done on surroundings (expanding)

ΔE = ΔH ? TRUE When volume is constant ΔE = q – P(0) ΔE = q FALSE When pressure is constant Volume must change when pressure is constant BUT differences between ΔE & ΔH are very small at atmospheric pressure.

First Law of Thermodynamics The energy of the universe is constant Heat lost = heat gained Law of conservation of energy

Spontaneous Processes Occurs without outside intervention Variable speed Everything that happens begins with a spontaneous change somewhere!

Entropy (S) Measure of randomness or disorder Closely linked with probability Exothermic reactions tend to be spontaneous Increase in entropy tends to be spontaneous S solid < S liquid <<< S gas

Second Law of Thermodynamics In any spontaneous process there is always an increase in the entropy of the universe. S universe is increasing! ΔS = S products – S reactants S(+) entropy increases S(-) entropy decreases

Predict ΔS sign: H 2 O (s)  H 2 O (l) CO 2 (g)  CO 2 (s) NaCl (s)  NaCl (aq) 2 NaHCO 3(s)  NaCO 3(s) + CO 2 (g) + H 2 O (g) O 2 (g) + 2 SO 2 (g)  2 SO 3(g)

1.Yes. Nonspontaneous processes can never occur. 2.No. Nonspontaneous processes can occur with some external assistance.