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Draw and describe the following molecule: Chemistry 6A F2007 8 + 4×(2) Dr. J.A. Mack = 16 electrons needed 5 + 4×(1) − 1 = 8 electrons needed 16 − 8 = 8 electrons shared 4 bonds N must go into the center since H can only have one bond H N remove one for the charge! Tetrahedral shape! + H 10/19/07 NH +4 H H 10/19/07 Dr. Mack. CSUS 1 What is the net ionic equation for the reaction of aqueous lithium hydroxide and aqueous nitric acid? H H N H Dr. Mack. CSUS 2 Which of the following chemical equations is an acid-base reaction? Molecular Equation: a) 2 HCl(aq) + Zn(s) → H2(g) + ZnCl2(aq) b) HCl(aq) + NH3(aq) → NH4Cl(aq) LiOH(aq) + HNO3(aq) → H2O(l) + LiNO3(aq) balanced? yes! Ionic Equation: c) HCl(aq) + AgNO3(aq) → AgCl(s) + HNO3(aq) d) Ba(OH)2(aq) + Na2SO4(aq) → BaSO4(s) + 2 NaOH(aq) e) 2 NaOH(aq) + CuCl2(aq) → Cu(OH)2(s) + 2 NaCl(aq) Li+(aq) + OH−(aq) + H+(aq) + NO3− (aq) → Net Ionic Equation: If you chose “b” you are correct! H2O(l) + Li+(aq) + NO3− (aq) a) is a RedOx reaction and c) to e) are precipitation reactions! OH−(aq) + H+(aq) → H2O(l) 10/19/07 10/19/07 + H Dr. Mack. CSUS 3 10/19/07 Dr. Mack. CSUS 4 1 Which species in the reaction below undergoes reduction? All of the following are oxidation-reduction reactions EXCEPT Sn(s) + 2 H+(aq) → Sn2+(aq) + H2(g) 0 +1 +2 +2, −2 0 +1, −2 +2, −2, +1 a) CaO(s) + H2O(l) → Ca(OH)2(aq) b) H2(g) + Br2(g) → 2 HBr(g) c) Ca(s) + 2 HCl(aq) → CaCl2(aq) + H2(g) What is the oxidation number of phosphorus in P2O5? d) 2 NaBr(aq) + F2(g) → 2 NaF(aq) + Br2(g) O = −2 10 ÷ 2 = +5 P2O5 e) 2 H2O(l) → 2 H2(g) + O2(g) 5×(−2) = −10 If you chose “a” you are correct! P = +5 10/19/07 Dr. Mack. CSUS 5 Predict the products of the following reactions: + Cl2(g) → MgCl2(s) 6 All chemical processes are accompanied by energy changes: balanced? Yep! If a reaction gives off energy (heat heat), it is an exothermic reaction. Solutions of nitric acid and sodium carbonate are mixed… Reactants 2 HNO3(aq) + Na2CO3(aq) → H2O(l) + CO2(g) + 2 NaNO3(aq) balanced? Which is an acid neutralization reaction? Dr. Mack. CSUS Energy and Chemical Reactions magnesium metal reacts with chlorine gas to form… Mg(s) 10/19/07 Nope! Products + Energy If a reaction absorbs energy (heat heat), it is an endothermic reaction. Energy + Reactants Products Energy can be treated as part of the reactants or products! products 10/19/07 Dr. Mack. CSUS 7 10/19/07 Dr. Mack. CSUS 8 2 Thermochemical Equations: Energy and Chemical Reactions Reactants E (Products) Energy When the reaction is reversed , the sign of ∆H reverses: Products E (Reactants) ∆ERXN > 0 ∆ERXN < 0 E (Reactants) E (Products) When the products are higher in energy than the reactants, the rxn is: When the products are lower in energy than the reactants, the rxn is: 9 The amounts of substances and heat are expressed per moles. 1 mole + Cl2(g) → 2HCl(g) 1 mole CO2(g) + 2H2O(g) → CH4(g) + 2O2(g) ∆H = + 802 kJ Endothermic Dr. Mack. CSUS H2(g) ∆H = − 802 kJ Exothermic Exothermic Endothermic 10/19/07 CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + 185 kJ 10/19/07 10/19/07 They are the numbers in front of the chemical formulas. 2 mole They give the ratio of reactants and products. 1mol H 2 185kJ 103 J × × = 2.17 × 106 J 2.02g H 2 1mol H 2 1kJ Dr. Mack. CSUS 11 Stoichiometric balancing coefficients How many kJ of energy are released when 23.7 g of hydrogen are reacted with excess chlorine to form hydrogen chloride. 23.7g H 2 × Dr. Mack. CSUS Conversion factors ratio The balancing coefficients allow us to convert between numbers of reactants and products. 12 10/19/07 Dr. Mack. CSUS 13 3 Since the individual ratios must scale to moles, we can write: Stoichiometry: The branch of chemistry that deals with the mole proportions of chemical reactions. Stoichiometric ratio: The ratio of any two species (reactants or products) in a balanced chemical reaction. 2A + 3B A2B3 2A 2 mols A 3B 3 mols B The molar ratios allow us to relate the amounts of reactants and products in a chemical equation. 2 A’s combine with 3B’s CONVERSION FACTORS!!! 2A 3B 3B 10/19/07 i.e. 14 Consider the following reaction: 10/19/07 = 2 mols A 3 mols B 2 mol 3 H2(g) + N2(g) 16 2 NH3(g) Write all of the molar ratio conversion factors for this reaction: how many should there be? 1 mol N 2 3 mol H 2 Dr. Mack. CSUS 15 ammonia is formed from its elements: N2(g) + 3H2(g) → 2NH3(g) 3 mol Dr. Mack. CSUS Consider the following reaction: ammonia is formed from its elements: 10/19/07 2 mols A 2A Dr. Mack. CSUS 1 mol 3 mols B × 10/19/07 six… 3 × 2 3mol H 2 1mol N 2 1mol N 2 2mol NH 3 3mol H 2 2mol NH 3 1mol N 2 3mol H 2 2mol NH 3 1mol N 2 2mol NH 3 3mol H 2 Dr. Mack. CSUS 17 4 Give the following reaction Given the following reaction, how many moles of nitrogen are needed to completely react 9 moles of hydrogen? 3 H2(g) 9 mol H2 + N2(g) 1mol N 2 3mol H 2 × 2C2H6 (g) + 7 O2(g) 3 mol of N2 10/19/07 × Dr. Mack. CSUS 4CO2(g) + 6H2O(l) How many moles of water are produced when 3 mols of oxygen react? 2 NH3(g) 3.0 mol O 2 × = 3 mol of N2 2 sig. figs. How many mols of ammonia will be produced? 2mol NH 3 1mol N 2 → 6 mol H 2O 7 mol O 2 exact conversion factor = 2.6mol H 2O 2 sig. figs. How many moles of C2H6 must react to produce 1.75 mols of CO2? = 6 mol NH3 1.75 mol CO2 × 18 10/19/07 2 mol C2 H 6 = 0.875 mol C2H6 4 mol CO 2 Dr. Mack. CSUS 19 5