NH + Chemistry 6A F2007. Dr. J.A. Mack 10/19/07. Draw and describe the following molecule: (2) = 16 electrons needed

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1 Chemistry 6A F007 Dr. J.A. Mack 10/19/07 10/19/07 Dr. Mack. CSUS 1 Draw and describe the following molecule: 8 + 4() = 16 electrons needed 5 + 4(1) 1 = 8 electrons needed 16 8 = 8 electrons shared N must go into the center since can only have one bond 4 bonds N + 4 remove one for the charge! N N + Tetrahedral shape! 10/19/07 Dr. Mack. CSUS + What is the net ionic equation for the reaction of aqueous lithium hydroxide and aqueous nitric acid? Molecular Equation: LiO(aq) + NO (aq) balanced? Ionic Equation: Li + (aq) + O (aq) + + (aq) + NO (aq) O(l) + LiNO (aq) yes! Which of the following chemical equations is an acid-base reaction? a) Cl(aq) + Zn(s) (g) + ZnCl (aq) b) Cl(aq) + N (aq) N 4 Cl(aq) c) Cl(aq) + AgNO (aq) AgCl(s) + NO (aq) d) Ba(O) (aq) + Na SO 4 (aq) BaSO 4 (s) + NaO(aq) e) NaO(aq) + CuCl (aq) Cu(O) (s) + NaCl(aq) Net Ionic Equation: O (aq) + + (aq) O(l) + Li + (aq) + O(l) NO (aq) If you chose b you are correct! a) is a RedOx reaction and c) to e) are precipitation reactions! 10/19/07 Dr. Mack. CSUS 10/19/07 Dr. Mack. CSUS 4

2 Which species in the reaction below undergoes reduction? Sn(s) + + (aq) Sn + (aq) + (g) What is the oxidation number of phosphorus in P O 5? 10 = +5 P = +5 O = P O 5 5( ) = 10 All of the following are oxidation-reduction reactions EXCEPT +, +1, +,, +1 a) CaO(s) + O(l) Ca(O) (aq) b) (g) + Br (g) Br(g) c) Ca(s) + Cl(aq) CaCl (aq) + (g) d) NaBr(aq) + F (g) NaF(aq) + Br (g) e) O(l) (g) + O (g) If you chose a you are correct! 10/19/07 Dr. Mack. CSUS 5 10/19/07 Dr. Mack. CSUS 6 Predict the products of the following reactions: magnesium metal reacts with chlorine gas to form Mg(s) + Cl (g) MgCl (s) balanced? Solutions of nitric acid and sodium carbonate are mixed Yep! NO (aq) + Na CO (aq) O(l) + CO (g) + NaNO (aq) Energy and Chemical Reactions All chemical processes are accompanied by energy changes: If a reaction gives off energy (heat), it is an exothermic reaction. Reactants Products + Energy If a reaction absorbs energy (heat), it is an endothermic reaction. Which is an acid neutralization reaction? balanced? Nope! Energy + Reactants Products Energy can be treated as part of the reactants or products! 10/19/07 Dr. Mack. CSUS 7 10/19/07 Dr. Mack. CSUS 8

3 Energy and Chemical Reactions Reactants Products Thermochemical Equations: When the reaction is reversed, the sign of reverses: Energy E (Products) E (Reactants) E RXN > 0 E RXN < 0 E (Reactants) E (Products) C 4 (g) + O (g) CO (g) + O(g) = 80 kj Exothermic When the products are higher in energy than the reactants, the rxn is: Endothermic When the products are lower in energy than the reactants, the rxn is: Exothermic CO (g) + O(g) C 4 (g) + O (g) = + 80 kj Endothermic 10/19/07 Dr. Mack. CSUS 9 10/19/07 Dr. Mack. CSUS 11 The amounts of substances and heat are expressed per moles. (g) + Cl (g) Cl(g) kj 1 mole 1 mole mole ow many kj of energy are released when.7 g of hydrogen are reacted with excess chlorine to form hydrogen chloride. Stoichiometric balancing coefficients They are the numbers in front of the chemical formulas. They give the ratio of reactants and products. ratio Conversion factors.7g 1mol.0g 185kJ 1mol 10 J 1kJ 6 = J The balancing coefficients allow us to convert between numbers of reactants and products. 10/19/07 Dr. Mack. CSUS 1 10/19/07 Dr. Mack. CSUS 1

4 Stoichiometry: The branch of chemistry that deals with the mole proportions of chemical reactions. Since the individual ratios must scale to moles, we can write: Stoichiometric ratio: The ratio of any two species (reactants or products) in a balanced chemical reaction. A + B A B A B mols A mols B A s combine with B s CONVERSION FACTORS!!! A B B A 10/19/07 Dr. Mack. CSUS 14 The molar ratios allow us to relate the amounts of reactants and products in a chemical equation. i.e. mols B mols A mols B = mols A 10/19/07 Dr. Mack. CSUS 15 Consider the following reaction: N (g) ammonia is formed from its elements: (g) + (g) N 1 mol mol mol 1 mol N mol 10/19/07 Dr. Mack. CSUS 16 N (g) Consider the following reaction: ammonia is formed from its elements: (g) + N (g) N (g) Write all of the molar ratio conversion factors for this reaction: how many should there be? six mol mol mol N mol N 10/19/07 Dr. Mack. CSUS 17 mol mol N mol N mol

5 Given the following reaction, how many moles of nitrogen are needed to completely react 9 moles of hydrogen? (g) + N (g) N (g) 9 mol mol 10/19/07 Dr. Mack. CSUS 18 = mol of N ow many mols of ammonia will be produced? mol of N mol N = 6 mol N Give the following reaction C 6 (g) + 7 O (g) 4CO (g) + 6 O(l) ow many moles of water are produced when mols of oxygen react? 6 mol O.0 mol O =.6mol O 7 mol O sig. figs. exact sig. figs. conversion factor ow many moles of C 6 must react to produce 1.75 mols of CO? mol C mol CO = mol C 4 mol CO 6 10/19/07 Dr. Mack. CSUS 19

What is one of the spectator ions (with correct coefficient)? A)

What is one of the spectator ions (with correct coefficient)? A) Chem 101 Exam Fall 01 Section 001 1. Based on the solubility rules Mg (PO 4 ) is A) soluble B) insoluble. An aqueous solution of potassium sulfate is allowed to react with an aqueous solution of What is