 Students will…..  Write chemical reactions using words and chemical symbols.  Balance chemical equations using lowest whole number ratios.  Identify, complete and balance combination rxns, decomposition rxns, combustion rxns, single-replacement rxns, and double-replacement rxns.  Use the activity series of metals to determine whether or not a single replacement reaction will occur.  Determine what element is oxidized and what element is reduced in a single replacement reaction.  Use solubility rules to determine the products of double-replacement reactions.  Write net ionic equations for aqueous reactions.

 Students will…..  Write chemical reactions using words and chemical reactions.  Balance chemical equations using lowest whole number ratio. Assignments to be Completed:  ChemQuest 29 (Balancing Equations)  Balancing Equations WS #1  Writing and Balancing WS #2  Textbook pp #1-10

Chemical Equations A chemical equation uses formulas to express the identities and quantities of substances involved in a physical or chemical change. The formation of HF gas on the macroscopic and molecular levels.

A three-level view of the reaction between magnesium and oxygen.

Features of Chemical Equations Mg + O 2 MgO Reactants are written on the left. A yield arrow points from reactants to products. Products are written on the right. The equation must be balanced; the same number and type of each atom must appear on both sides.

translate the statement balance the atoms using coefficients; formulas cannot be changed Start with metals, followed by nonmetals. If there is a polyatomic ion, keep it together. Once a coefficient has been placed in front of a chemical formula, make changes to the other side of the equation to balance what was changed by the coefficient. If doing a combustion reaction, the order should be carbon, hydrogen, oxygen. specify states of matter adjust coefficients if necessary check that all atoms balance Balancing a Chemical Equation magnesium and oxygen gas react to give magnesium oxide: Mg + O 2 → MgO 2Mg + O 2 → 2MgO 2Mg (s) + O 2 (g) → 2MgO (s)

 Aluminum foil is heated in the presence of oxygen gas to produce solid aluminum oxide.  Silver nitrate solution is added to a solution of potassium phosphate to produce silver phosphate precipitate and aqueous potassium nitrate.  Iron is added to hydrochloric acid to produce aqueous iron(III) chloride and hydrogen gas.  Propane gas is burned in the presence of oxygen gas to produce carbon dioxide gas and gaseous water.

translate the statement Sample Problem Balancing Chemical Equations PROBLEM: PLAN:SOLUTION: balance the atoms specify states of matter Within the cylinders of a car’s engine, the hydrocarbon octane (C 8 H 18 ), one of many components of gasoline, mixes with oxygen from the air and burns to form carbon dioxide and water vapor. Write a balanced equation for this reaction. adjust the coefficients check the atoms balance C 8 H 18 + O 2 CO 2 + H 2 O 2C 8 H O 2 16CO H 2 O 2C 8 H 18 (l) + 25O 2 (g) 16CO 2 (g) + 18H 2 O (g) C 8 H 18 + O 2 8 CO H 2 O 25 2

Molecular Scene Combustion of Octane

Sample Problem Balancing an Equation from a Molecular Scene PROBLEM:The following molecular scenes depict an important reaction in nitrogen chemistry. The blue spheres represent nitrogen while the red spheres represent oxygen. Write a balanced equation for this reaction. PLAN:Determine the formulas of the reactants and products from their composition. Arrange this information in the correct equation format and balance correctly, including the states of matter.

SOLUTION: The reactant circle shows only one type of molecule, composed of 2 N and 5 O atoms. The formula is thus N 2 O 5. There are 4 N 2 O 5 molecules depicted. The product circle shows two types of molecule; one has 1 N and 2 O atoms while the other has 2 O atoms. The products are NO 2 and O 2. There are 8 NO 2 molecules and 2 O 2 molecules shown. Sample Problem The reaction depicted is 4 N 2 O 5 → 8 NO O 2. Writing the equation with the smallest whole-number coefficients and states of matter included; 2 N 2 O 5 (g) → 4 NO 2 (g) + O 2 (g)