Chemical Reactions Chapter

3.1 Chemical Equations the reactants are written to the left and the products are written to the right of the arrow the reactants are written to the left and the products are written to the right of the arrow s, g, l, aq indicate the states of matter s, g, l, aq indicate the states of matter coefficients are used to show the relative amounts coefficients are used to show the relative amounts the law of conservation of matter (Antoine Lavoisier) the law of conservation of matter (Antoine Lavoisier)

Chemical Equations balanced equations vs. skeleton equations balanced equations vs. skeleton equations relationship between amounts is stoichiometry relationship between amounts is stoichiometry –stoichiometric coefficients indicate number of atoms, molecules, formula units, or moles

3.2 Balancing Formulas for reactants and products have to be written correctly Formulas for reactants and products have to be written correctly Subscripts cannot be changed to balance Subscripts cannot be changed to balance

Balancing Combustion Step 1: write correct formulas for reactants and products Step 1: write correct formulas for reactants and products Step 2: balance the carbon atoms Step 2: balance the carbon atoms Step 3: balance the hydrogen atoms Step 3: balance the hydrogen atoms Step 4: balance the oxygen atoms Step 4: balance the oxygen atoms Step 5: verify atoms are balanced Step 5: verify atoms are balanced

Combustion Reactions Complete oxidation of an organic compound to yield CO 2 and H 2 O Complete oxidation of an organic compound to yield CO 2 and H 2 O –C 2 H 4(g) + 3O 2(g)  2CO 2(g) + 2H 2 O (l) Nonmetallic hydrides combine with oxygen to form oxides and water Nonmetallic hydrides combine with oxygen to form oxides and water –SiH 4(g) + 2O 2(g)  SiO 2(s) + 2H 2 O (l) Nonmetallic sulfides combine with oxygen to form sulfur dioxide and oxides Nonmetallic sulfides combine with oxygen to form sulfur dioxide and oxides –CS 2(s) + 3O 2(g)  CO 2(g) + 2SO 2(g)

3.3 Chemical Equilibrium Reactions are reversible, and many reactions lead to incomplete conversion of reactants to products. Reactions are reversible, and many reactions lead to incomplete conversion of reactants to products. Chemical equilibrium is when no macroscopic change is observed. Chemical equilibrium is when no macroscopic change is observed. Dynamic equilibrium indicates the forward and reverse reactions are occurring at equal rates. Dynamic equilibrium indicates the forward and reverse reactions are occurring at equal rates.

Chemical Equilibrium Depending upon different factors, product-favored reactions are reactions in which reactants are largely converted to products at equilibrium. Depending upon different factors, product-favored reactions are reactions in which reactants are largely converted to products at equilibrium. Reactant-favored reactions mean that at equilibrium only a small amount of reactants have been converted to products. Reactant-favored reactions mean that at equilibrium only a small amount of reactants have been converted to products.

3.4 Reactions in Aqueous Solution Another name for a solution is a homogeneous mixture. Another name for a solution is a homogeneous mixture. –solute and solvent Substance dissolved in water are called aqueous solutions. Substance dissolved in water are called aqueous solutions. Polarity of water creates an attraction for ions. Polarity of water creates an attraction for ions. –Water molecules surround each ion in the dissolved substance.

Reactions in Aqueous Solutions Four major categories of chemical reactions: Four major categories of chemical reactions: –synthesis –decomposition –oxidation-reduction –acid-base reactions

3.5 Ions and Molecules Compounds that conduct electricity in aqueous solution are called electrolytes. Compounds that conduct electricity in aqueous solution are called electrolytes. –All ionic compounds that are soluble in water are electrolytes. Strong electrolytes completely ionize in solution. (such as salt) Strong electrolytes completely ionize in solution. (such as salt) Weak electrolytes only partially dissociate. (such as acetic acid) Weak electrolytes only partially dissociate. (such as acetic acid) Nonelectrolytes dissolve in water but don’t ionize. (such as sugar) Nonelectrolytes dissolve in water but don’t ionize. (such as sugar) –Most molecular compounds that dissolve in water are nonelectrolytes.

Solubility of Ionic Compounds in Water Although many ionic compounds dissolve completely, some dissolve only to a small extent and some are essentially insoluble. Although many ionic compounds dissolve completely, some dissolve only to a small extent and some are essentially insoluble. Solubility rules on page 126 Solubility rules on page 126

3.6 Precipitation Reactions precipitation reactions form insoluble products (precipitate) precipitation reactions form insoluble products (precipitate) lead nitrate and potassium iodide lead nitrate and potassium iodide products can be predicted using solubility rules products can be predicted using solubility rules

Net Ionic Equations net ionic equations leave out the spectators net ionic equations leave out the spectators –charge balance and mass balance –Only aqueous ions, insoluble compounds, and weak or nonelectrolytes (such as sugar, weak acids/bases, or gases) that participate in a chemical reaction are included in the net ionic equation.

Net Ionic Equations All AP equations “work”. The equations need to be written in net ionic form. All spectators must be left out and all ions written with charges. All molecular substances and insoluble compounds must be written together (not ionized). Weak electrolytes are not ionized, solids and pure liquids are written together. All AP equations “work”. The equations need to be written in net ionic form. All spectators must be left out and all ions written with charges. All molecular substances and insoluble compounds must be written together (not ionized). Weak electrolytes are not ionized, solids and pure liquids are written together.

Net Ionic Equations First classify the reaction as to type. If there is an acidic or basic solution, then it is redox. All solutions do not fit neatly into the five types you’ve already learned. Save all the reactions that you do and practice them before the AP test in May. First classify the reaction as to type. If there is an acidic or basic solution, then it is redox. All solutions do not fit neatly into the five types you’ve already learned. Save all the reactions that you do and practice them before the AP test in May.

Practice Problems Write a balanced net ionic equation for each of the following reactions: Write a balanced net ionic equation for each of the following reactions: –AlCl 3 + Na 3 PO 4  AlPO 4 + NaCl –Solutions of iron (III) chloride and potassium hydroxide give iron (III) hydroxide and potassium chloride when combined. –Solutions of lead (II) nitrate and potassium chloride give lead (II) chloride and potassium nitrate when combined.

Homework After reading Sections , you should be able to do the following… After reading Sections , you should be able to do the following… P. 154 (33-36) P. 154 (33-36)