4/16/13 Objective Review ionic and covalent bonding Identify the signs of a chemical reaction and discuss chemical equations 4/15/13

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1 4/15/13 Illustrate bonding Describe the signs of a chemical reaction and discuss chemical equations Find the charge of the ions below: (int: Ignore the neutrons and compare p and e) 1.5 protons, 6 electrons, and 5 neutrons. 2.8 protons, 7 neutrons, 7 electrons 3.12 protons, 12 electrons, and 8 neutrons 4.17 protons, 14 electrons, and 15 neutrons 4/16/13 Review ionic and covalent bonding Identify the signs of a chemical reaction and discuss chemical equations Determine what type of bond the following compounds have and then draw the Lewis structure 1. 2 O 2. C 2 6 Equations & You should be able to assify by type. Write a balanced molecular equation, complete ionic equation, and a net ionic equation. Balance oxidation-reduction. Predict if a precipitate will form using the solubility rules. Predict products of given the chemical names of the reactants. Organize Your Thoughts Describing a Reaction Indications of a Reaction equations equations Evolution of heat, light, and/or sound Production of a gas Balancing equations Predicting products from reactants Synthesis Decomposition Single replacement Double replacement Combustion Formation of a precipitate Color change Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175 1

2 Signs of Equations : Shows reactants (what goes in)and products (what comes out) and the amounts. release 4 Al(s) 3 O 2 (g) 2 Al 2 O 3 (s) aluminum oxide input The letters (s), (g), and (l) are the physical states of compounds. change in color change in odor production of new gases or vapor input or release of energy difficult to reverse The numbers in the front are called coefficients. (tell us how much) 4/17/13 s Simulate the law of conservation of matter Correctly balance a chemical equation According to the law of conservation of matter, if I start with the following amounts, what will I end up with? 3 oxygen and 2 aluminum 1 sodium and 1 chlorine Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. The Law of Conservation of Matter 100% 100% Factory 20% 80% Kotz web Conservation of Mass Lab 4/18/13 Accurately balance chemical equations Based on your findings from yesterday s lab, why did the mass decrease when you opened the bag? 2

3 Characteristics of Equations Because of the principle of the conservation of matter, An equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788 The equation must represent known facts. The equation must contain the correct formulas for the reactants and products. The law of conservation of mass must be satisfied. Unbalanced and Balanced Equations Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane oxygen Reactant Product C 4 2 O 2 CO O carbon dioxide water 2 2 (unbalanced) reactants 2 2 products (balanced) reactants products Balancing Equations Balanced Equation number of atoms in reactant equal the number of atoms in the product Determine whether the following equation is balanced. 2 2 O 2 O O 2 O 2 Write a word equation for the reaction. Write the correct formulas for all reactants and products. Determine the coefficients that make the equation balance. Balance Oxygen last! 3

4 Balancing Equations Other examples NO(g) O 2 (g) NO 2 (g) is it balanced? Balancing Equations An important point to remember 2 NO(g) O 2 (g) 2NO 2 (g) Is this balanced? NO(g) O(g) NO 2 (g) Is this OK? Is this balanced? NO(g) ½ O 2 (g) NO 2 (g) Is this OK? The 2 to the left of NO(g) and NO 2 (g) refers to the number of molecules present in the balanced equation. It is a multiplier for every atom in the molecule. The subscript 2 in O 2 (g) and NO 2 (g) refers to the number of atoms of this type that are present in each molecules (or ionic compound). Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. C 4 2 O 2 CO O 1) Write a word equation for the reaction. chlorine sodium bromide bromine sodium chloride 2) Write the correct formulas for all reactants and products. 2 Br Br 2 3) Determine the coefficients that make the equation balance. 2 2 Br Br 2 2 Reactants Products 1 C atom 1 C atom 4 atoms 4 atoms 4 O atoms 4 O atoms Reactants Products Balancing Equations Lab C(s) O 2 (g) CO 2 (g) carbon oxygen carbon dioxide Reactants Product 1 carbon atom 1 carbon atom 2 oxygen atoms 2 oxygen atoms catalyst speeds up reaction Pt Pt 2 2 (g) O 2 (g) 2 2 O (l) hydrogen oxygen water Reactants Product 24 hydrogen atoms 2 4 hydrogen atoms 2 oxygen atoms 1 2 oxygen atoms Un balanced 4

5 Symbols Used in Equations Symbols Used in Equations Yields ; indicates result of reaction Used to indicate a reversible reaction Reactants are heated (s) A reactant or product in the solid state; also used to indicate a precipitate 2 atm Pressure at which reaction is carried out, in this case 2 atm Alternative to (s), but used only to indicate a precipitate pressure Pressure at which reaction is carried out exceeds normal atmospheric pressure (l) A reactant or product in the liquid state 0 o C Temperature at which reaction is carried out, in this case 0 o C (aq) A reactant or product in an aqueous solution (dissolved in water) MnO 2 Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction (g) A reactant or product in the gaseous state 4/23/13 Define types of oxidation reduction Analyze the results of a oxidation reduction reaction : Balance the following P 4 O 2 P 2 O 3 C 4 O 2 CO 2 2 O Types of Reduction-Oxidation (Redox) Synthesis reaction Decomposition Reaction A B AB AB A B Combustion reaction (of a hydrocarbon) C O 2 CO 2 2 O Precipitation Single-replacement reaction A BC AC B compound element compound element Double-replacement reaction AB CD AD CB Acid-Base compound compound compound compound Acid/Base reaction X BO BX O acid base salt water Oxidation-Reduction (Redox) These involve the loss of electrons by one compound, and the gain of electrons by another compound. F F OIL RIG Oxidation: losing e - Reduction: gaining e - Synthesis Reaction of two or more elements to form a compound General form: A B AB element or element or compound compound compound 5

6 Synthesis Reaction Synthesis General form: A B AB - element or element or compound compound compound Photosynthesis 6 CO O C 6 12 O 6 6 O 2 Formation of water 2 2 O O Formation of salt General Form A B C Decomposition Reaction When a large molecule decomposes (breaks up) into smaller elements or compounds 2 2 O 2 2 O 2 O O General form: AB A B compound two or more elements or compounds Decomposition ydrogen Peroxide 2 2 O O O 2 Electrolysis of water electricity 2 2 O 2 2 O 2 Nitrogen triiodide 2 NI 3 N 2 3 I 2 General Form AB A B Introduction to Redox Rxns Lab 4/24/13 Gain of electrons: reduction Loss of electrons: oxidation Reducing agent: atom that gives up electrons Oxidizing agent: atom that takes away electrons Describe precipitation (single and double replacement) and acid/base. Demonstrate ability to balance equations What is the general formula for a synthesis reaction? For a decomposition reaction? 6

7 Single Replacement Double Replacement An element may react with a compound to produce a different element and a new compound Two compounds react and the cation in one compound replaces the cation in the second compound. Single-replacement reaction Mg CuSO 4 MgSO 4 Cu General form: A BC AC B Double-replacement reaction CaCO 3 2 Ca 2 2CO 3 General form: AB CD AD CB Acid/Base When an acid (proton donor) and a base (proton acceptor) react to form a conjugate acid and conjugate base. Summary of asses of When equal amounts of acid and base react we call Acid this a neutralization reaction 2 0 N 3 N 4 O - Base Conjugate acid Conjugate base Precipitation Combustion Oxidation-Reduction Synthesis (Reactants are elements.) Acid-Base Decomposition (Products are elements.) 7