Section 8.1 Understanding Reactions in Aqueous Solutions

Section 8.1 Understanding Reactions in Aqueous Solutions CHAPTER 7.2: Chemical reactions involve a rearrangement of the ways atoms are grouped together. A chemical equation represents a chemical reaction. –Reactants are shown to the left of an arrow. –Products are shown to the right of the arrow.

Section 8.1 Understanding Reactions in Aqueous Solutions In a chemical reaction atoms are not created or destroyed. All atoms present in the reactants must be accounted for in the products. Same number of each type atom on both sides of the arrow

Section 8.1 Understanding Reactions in Aqueous Solutions Balancing a Chemical Equation CH 4 + O 2  CO 2 + H 2 O Unbalanced equation Balancing the equation The balanced equation CH 4 + 2O 2  CO 2 + 2H 2 O

Section 8.1 Understanding Reactions in Aqueous Solutions Physical states of compounds are often given in a chemical equation.

Section 8.1 Understanding Reactions in Aqueous Solutions CHAPTER 7.3: A chemical reaction is balanced by using a systematic approach: –Write the formulas of the reactants and products to give the unbalanced chemical equation. –Balance by trial and error starting with the most complicated molecule(s). Going back & forth start with – “One-sies” – 2 nd to last: oxygens – Last: hydrogens –When done, check to be sure the equation is balanced (same numbers of all types of atoms on the reactant and product sides).

Section 8.1 Understanding Reactions in Aqueous Solutions Example: H 2 (g) + O 2 (g)  H 2 O(l) Hydrogen gas and oxygen gas combine to form liquid water. –Balance by trial and error starting with the most complicated molecule(s).

Section 8.1 Understanding Reactions in Aqueous Solutions Example: Hydrogen gas and oxygen gas combine to form liquid water. –At the end check to be sure the equation is balanced (same numbers of all types of atoms on the reactant and product sides). 2H 2 (g) + O 2 (g)  2H 2 O(l) –END OF CHAPTER 7!

Section 8.1 Understanding Reactions in Aqueous Solutions CHAPTER 8: Section 8.1 A. Predicting Whether a Reaction Will Occur Four driving forces favor a chemical change. –Formation of a solid –Formation of water –Transfer of electrons –Formation of a gas

Section 8.1 Understanding Reactions in Aqueous Solutions B. Reactions in Which a Solid Forms A reaction in which a solid forms is called a precipitation reaction. –Solid = precipitate

Section 8.1 Understanding Reactions in Aqueous Solutions The ions separate and move around independently. B. Reactions in Which a Solid Forms What Happens When an Ionic Compound Dissolves in Water?

Section 8.1 Understanding Reactions in Aqueous Solutions B. Reactions in Which a Solid Forms What Happens When an Ionic Compound Dissolves in Water? K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq)  Products

Section 8.1 Understanding Reactions in Aqueous Solutions Determine the possible products from the ions in the reactants. In our example K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq)  Products The possible ion combinations are B. Reactions in Which a Solid Forms How to Decide What Products Form

Section 8.1 Understanding Reactions in Aqueous Solutions B. Reactions in Which a Solid Forms Solubility Rules

Section 8.1 Understanding Reactions in Aqueous Solutions B. Reactions in Which a Solid Forms Predicting Precipitates Using Solubility Rules –Soluble solid = sol –Insoluble solid = insol –Slightly soluble solid = ss

Section 8.1 Understanding Reactions in Aqueous Solutions B. Reactions in Which a Solid Forms

Section 8.2 Other Reactions in Aqueous Solutions A. Reactions That Form Water: Acids and Bases Arrhenius Acids and Bases A strong acid is one in which virtually every molecule dissociates (ionizes) in water to an H + ion and an anion.

Section 8.2 Other Reactions in Aqueous Solutions A strong base is a metal hydroxide that is completely soluble in water, giving separate OH  ions and cations. A. Reactions That Form Water: Acids and Bases Arrhenius Acids and Bases –Most common  NaOH, KOH

Section 8.2 Other Reactions in Aqueous Solutions A. Reactions That Form Water: Acids and Bases Arrhenius Acids and Bases The products of the reaction of a strong acid and a strong base are water and a salt. –Salt  Ionic compound = metal + nonmetal M + + X - -- Water formation equation: H + (aq) + OH − (aq)  H 2 O(l) Note: The reaction of H + and OH − is called an acid-base reaction. –H +  acidic ion –OH −  basic ion

Section 8.2 Other Reactions in Aqueous Solutions B. Reactions of Metals with Nonmetals (Oxidation- Reduction) Reactions between metals and nonmetals involve a transfer of electrons from the metal to the nonmetal. This is called an oxidation – reduction reaction.

Section 8.3 Classifying Reactions A. Ways to Classify Reactions Driving forces for a reaction: –Formation of a solid AB + CD  AD + CB Precipitation reaction Double displacement reaction –Formation of water H + (aq) + OH − (aq)  H 2 O(l) Acid-base reaction

Section 8.3 Classifying Reactions A. Ways to Classify Reactions Driving forces for a reaction: –Transfer of electrons –Formation of a Gas A + BC  B + AC Single replacement reaction

Section 8.3 Classifying Reactions Involve oxygen and produce energy so rapidly that a flame results Produces CO 2 + H 2 O Example –CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g) –Special class of oxidation-reduction reactions B. Other Ways to Classify Reactions Combustion Reactions

Section 8.3 Classifying Reactions A synthesis reaction is one in which a compound forms from simpler materials. One product, and two (or more) reactants Example –C(s) + O 2 (g)  CO 2 (g) –Special class of oxidation-reduction reactions B. Other Ways to Classify Reactions Synthesis (Combination) Reactions

Section 8.3 Classifying Reactions A decomposition reaction occurs when a compound is broken down into simpler substances. One reactant, and two (or more) products. Example –2H 2 O(l)  2H 2 (g) + O 2 (g) B. Other Ways to Classify Reactions Decomposition Reactions

Section 8.3 Classifying Reactions B. Other Ways to Classify Reactions Summary

Section 8.3 Classifying Reactions SUMMARY OF REACTION TYPES TO KNOW: Double displacement reaction AB + CD  AD + CB Acid-base reaction H + X - (aq) + M + OH − (aq)  M + X - + H 2 O(l) Single replacement reaction A + BC  B + AC Combustion reaction CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g) Synthesis reaction C(s) + O 2 (g)  CO 2 (g) one product Decomposition reaction one reactant 2H 2 O(l)  2H 2 (g) + O 2 (g)