Chemistry 102 Dr. Don DeCoste 367J Noyes Lab decoste@illinois.edu 3-4 pm Tuesdays and Thursdays By appointment; open door policy http://chem.illinois.edu

To Do Finish reading Chapter 3. Text homework for Chapter 3. Quiz #2 on Friday, February 12 Lon-Capa assignments #1, #2.

Clicker Question Substance AB2 is 42.86% A by mass. Determine the percent B by mass for substance A2B. a) 14.28% B b) 25.00% B c) 28.57% B d) 57.14% B e) I do not know/I can’t get any of the above answers.

Problem Solving Approach What are we trying to solve? That is “where are we going?” What does this mean? What do we know? That is, “where have we been?” What procedures do we know? That is, “how do we get there?” Requires knowledge and understanding!

Stoichiometry Determine the amount(s) of reactant(s) or product(s) given amount(s) of reactant(s) or product(s). We must have a balanced chemical equation. Reactions occur by numbers of atoms/molecules.

Balanced Chemical Equations Chemical reactions are rearrangements of atoms. Atoms are not changed in a chemical reaction.

Clicker Question When iron(III) oxide is heated with carbon, the products are iron metal and carbon monoxide. Balance the equation in standard form and determine the sum of the coefficients. a) 4 b) 5 c) 6 d) 8 e) 9

N2(g) + H2(g)  NH3(g)

N2(g) + 3H2(g)  2NH3(g)