Office Hours 367J Noyes Lab decoste@illinois.edu 11am-12pm Mondays and Wednesdays (after lecture) 10-11 am Tuesdays and 1-2 pm Thursdays By appointment; open-door policy

Office Hours No office hours Tuesday, September 27.

Don’t forget textbook homework! Lon-Capa 4th HW assignment due Friday, 10/7, 5 pm. It is open now. 3rd Quiz due Sunday, 10/9 by 10 pm. It will open Friday, 10/7 at 5 pm. Don’t forget textbook homework!

Three Big Topics Stoichiometry: information on “what” happens; allows us to determine amounts of reactants and products. Thermodynamics: information on “why” reactions happen; allows us to make predictions about whether a reaction will occur. Kinetics: information on “how” reactions happen (mechanisms); relates to the speed of reactions.

A Message From a Brilliant Man: “Thermodynamics is a funny subject. The first time you go through it, you don't understand it at all. The second time you go through it, you think you understand it, except for one or two small points. The third time you go through it, you know you don't understand it, but by that time you are so used to it, so it doesn't bother you any more.” Arnold Sommerfeld

“Ball on a Hill”

Some Big Ideas Low energy  low in potential energy  more stable. If a system absorbs energy, the natural tendency is to release it. That is, achieving low potential energy is “natural”. Ground state preferred over excited state. Energy is converted from one form to another but is NOT created nor destroyed. First law of thermodynamics. Energy is a state function (heat and work are not).

Questions To Consider How can we predict which reactions are spontaneous (and what do we mean by spontaneous)? How can we provide support (mathematical and qualitative) for observations? Ice cream melts Coffee cools Why do systems reach equilibrium? That is, why doesn’t the ball go “all the way down the hill”?

Clicker Question The freezing of water is an ________ process. a) exothermic b) endothermic c) I do not know.

Exothermic Process

Endothermic Process

Clicker Question The following chemical reaction is exothermic: A2 + B2  2AB. This means: more stable higher average bond energies a) Reactants Reactants b) Reactants Products c) Products Products d) Products Reactants e) I do not know.