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Midterm 2 Review

Midterm 2 Review - Chem 1A Midterm 2 Review Spencer Granett...

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1 Chem 1A Midterm 2 Review Spencer Granett and David Limmer, GSIs October 12, 2008 Unit 2: Change Changes in matter involve the reorganization of atoms, ions, and molecules depending on external conditions Chemical Reactions Patterns of chemical reactions Combination reactions 2Mg+O 2 2MgO Decomposition reactions CaCO 3 CaO + CO 2 Exchange reactions AgNO 3 (aq) + NaCl(aq) AgCl(s) + NaNO 3 (aq) Chemical Reactions Ions combine in ratios that maintain the charge neutrality of products 2 S 2 O 3 2 (aq) + I 2 (aq) S 4 O 6 2 (aq) + 2 I (aq) Stoichiometry Amounts are measured in moles The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12 1 mole = 6.022 x 10 23 iClicker question Consider the reaction If you start with 1 mole of N 2 and one mole of H 2 , how many moles of NH 3 will be formed? (Assume the reaction goes to completion) A 1/3 B 1/2 C 2/3 D 1 E 2 N 2 + 3 H 2 " 2 NH 3
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2 iClicker solution You must consider the stoichiometry of the reaction! Starting with 1 mol N 2 will yield 2 mol NH 3 Starting with 1 mol H 2 will yield 2/3 mol NH 3 H 2 is the limiting reagent The final yield will be 2/3 moles NH 3 N 2 + 3 H 2 " 2 NH 3 Reversible Reactions Some reactions are reversible The equilibrium constant of a reaction relates the ratios of products and reactants at equilibrium At equilibrium, forward and backward rates are equal Equilibrium Constants Different reactions have different values of K K is temperature dependent aA + bB " cC + dD K eq = [ C ] c [ D ] d [ A ] a [ B ] b Le Chatelier’s Principle A system in equilibrium subjected to a stress will react in a direction that relieves the stress iClicker question What happens if you add HCl? A the solution will turn more orange B the solution will turn more yellow C nothing will happen 2 H + + 2 CrO 4 2 " yellow # Cr 2 O 7 2 " orange + H 2 O iClicker question What happens if you double the volume by adding water?
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