Lecture 6

Readings

http://umdberg.pbworks.com/w/page/73084328/Example%3A%20Entropy%20and%20heat%20flow%20(2013)

http://umdberg.pbworks.com/w/page/63328761/Motivating%20free%20energy%20%282013%29

2nd Law

• Direction things chagne is so entropy of the total system increases

  • Total system = either the whole universe, or else an isolated system

• $Q$$Q$ = change in heat energy of an object

  • Its really a $\mathrm{\Delta }Q$$\Delta Q$ , but by convention we don't use a $\mathrm{\Delta }$$\Delta$ in front
  • If heat energy of an object goes up, $Q$$Q$ is positive
  • If heat energy of an object goes down, $Q$$Q$ is negative

• For a hot object near a cold object, $Q$$Q$ moves from hot to cold object:

• But because $T_C$$T_C$ is smaller than $T_H$$T_H$ , the entropy gained by cold object is greater than entropy lost by hot object, so net entropy of the system goes up.

Gibb's Free Energy

• Combines conservation of energy ( 1st Law ) with the direction of change ( 2nd Law ) , as we'll see in next lecture

• $\mathrm{\Delta }H=BondEnergy$$\Delta H = Bond\ Energy$

Multiple Choice