Announcements Be respectful – no electronics please! Post/Pre-lecture assignment due Tuesday Lab again on Monday Exam 1 grades posted Look at scaled score out of 100 points Get exams back in discussion tomorrow Liquid nitrogen ice cream winner is… Video: http://www.youtube.com/watch?v=G_Z3lmidmrY What is the purpose of the quicksand video?

Most Missed Multiple Choice

Session #1 Reflection Questions When you study for an exam, do you study to get an “A”, or do you study to learn? Which is more enjoyable, studying or learning? Why? Did you study a lot in high school? Approximately how many hours per week do you think you need to study at U of I? Are changes needed in your study habits and perspective? Merit Program, University of Illinois at Urbana-Champaign

So, What Can You Do to Ace Courses? Spend enough time reviewing and mastering the material. Aim for 100% mastery. Use your TAs, peers, and me for help if you do not understand how to solve a problem. When you make an appointment with yourself to study: KEEP IT Set a goal for study sessions. Smaller chunks and do them frequently!

“Read” the following reactions in words. 2P + 5O2  P2O5 2NaNO3  2NaNO2 + O2 2Al2O3(s) + 3C(s)  4Al(s) + 3CO2(g)

How Do We Balance Chemical Equations? Mainly trial and error (some general strategies though) Make sure you have same number of each type of atom on both sides of equation Do not balance by changing the subscripts! Balance the least complicated molecule LAST.

Discussion #1 Which of the following diagrams best represents the chemical equation N2 + H2 → NH3 after it is balanced? 1) + → 2) + → + 3) + + + + + + → 4) + + + → + 5) + + + →

Clicker #1 Which of the following shows the correctly balanced equation for this reaction: H2O2 → H2O + O2 A) 3 H2O2 → 3 H2O + O2 B) H2O2 → 2 H2O + O2 C) 2 H2O2 → 2 H2O + O2 D) H2O2 → H2O + O2

Example #2 Write and balance: solid magnesium reacts with nitrogen gas to form solid magnesium nitride.

Clicker #2 Solid magnesium reacts with oxygen gas to form solid magnesium oxide. Write and balance this equation, including phases. What is the sum of the coefficients when balanced in standard form? 3 4 5 6 7

Common Magnesium Compounds Magnesium Nitride Magnesium Oxide

Clicker #3 What is the correct unbalanced chemical equation for the reaction of iron(II) oxide with oxygen gas to produce iron(III) oxide? A) FeO + O2 → Fe2O3 B) FeO2 + O2 → Fe2O3 C) FeO2 + O2 → Fe3O2 D) FeO + O2 → Fe3O2 E) FeO2 + O2 → FeO

Na2SO4(aq) + Pb(NO3)2(aq)  PbSO4(s) + NaNO3(aq) Example #3 Balance the following equation in standard form: “Aqueous sodium sulfate reacts with aqueous lead(II) nitrate to produce solid lead(II) sulfate and aqueous sodium nitrate.” Na2SO4(aq) + Pb(NO3)2(aq)  PbSO4(s) + NaNO3(aq) 2

Example #3 Discussion What makes the following chemical equation an incorrect representation of the reaction below? Correct all parts that are incorrect. “Aqueous sodium sulfate reacts with aqueous lead(II) nitrate to produce solid lead(II) sulfate and aqueous sodium nitrate.” Na2SO4(aq) + Pb(NO3)2(l)  PbSO4(s) + Na2(NO3)2(aq)