Chapter Menu Chemical Reactions Section 9.1Section 9.1Reactions and Equations Section 9.2Section 9.2 Classifying Chemical Reactions Section 9.3Section 9.3 Reactions in Aqueous Solutions Exit Click a hyperlink or folder tab to view the corresponding slides.

Section 9-1 Section 9.1 Reactions and Equations Recognize evidence of chemical change. chemical change: a process involving one or more substances changing into a new substance chemical reaction reactant product chemical equation coefficient Represent chemical reactions with equations. Balance chemical equations. Chemical reactions are represented by balanced chemical equations.

Section 9-1 Chemical Reactions The process by which one or more substances are rearranged to form different substances is called a chemical reaction.chemical reaction

Section 9-1 Chemical Reactions (cont.) Evidence of a chemical reaction –Change in temperature –Change in color –Odor, gas, or bubbles may form.

Section 9-1 Representing Chemical Reactions Chemists use statements called equations to represent chemical reactions. Reactants are the starting substances.Reactants Products are the substances formed in the reaction.Products This table summarizes the symbols used in chemical equations.

Section 9-1 Representing Chemical Reactions (cont.) In word equations, aluminum(s) + bromine(l) → aluminum bromide(s) reads as “aluminum and bromine react to produce aluminum bromide”. Skeleton equations use symbols and formulas to represent the reactants and products. Al(s) + Br(l) → AlBr 3 (s) Skeleton equations lack information about how many atoms are involved in the reaction.

Section 9-1 Representing Chemical Reactions (cont.) A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.chemical equation

Section 9-1 Balancing Chemical Equations This figure shows the balanced equation for the reaction between aluminum and bromine.

Section 9-1 Balancing Chemical Equations (cont.) A coefficient in a chemical equation is the number written in front of a reactant or product, describing the lowest whole-number ratio of the amounts of all the reactants and products.coefficient

Section 9-1 Balancing Chemical Equations (cont.)

Section 9-1 Balancing Chemical Equations (cont.)

Section 9-1 Balancing Chemical Equations (cont.)

Section 9-1 Balancing Chemical Equations (cont.) The most fundamental law in chemistry is the law of conservation of mass. Balanced equations show this law.

Section 9-1 Balancing Chemical Equations (cont.)

Section 9-2 Section 9.2 Classifying Chemical Reactions Classify chemical reactions. metal: an element that is a solid at room temperature, a good conductor of heat and electricity, and is generally shiny Identify the characteristics of different classes of chemical reactions.

Section 9-2 Section 9.2 Classifying Chemical Reactions (cont.) synthesis reaction combustion reaction decomposition reaction single-replacement reaction There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions. double-replacement reaction precipitate

Section 9-2 Types of Chemical Reactions Chemists classify reactions in order to organize the many types. A synthesis reaction is a reaction in which two or more substances react to produce a single product.synthesis reaction

Section 9-2 Types of Chemical Reactions (cont.) When two elements react, the reaction is always a synthesis reaction.

Section 9-2 Types of Chemical Reactions (cont.) In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.combustion reaction Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.

Section 9-2 Decomposition Reactions A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds.decomposition reaction Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur.

Section 9-2 Replacement Reactions A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.single replacement reaction A + BX → AX + B

Section 9-2 Replacement Reactions (cont.) A metal will not always replace a metal in a compound dissolved in water because of differing reactivities. An activity series can be used to predict if reactions will occur.

Section 9-2 Replacement Reactions (cont.) Halogens frequently replace other halogens in replacement reactions. Halogens also have different reactivities and do not always replace each other.

Section 9-2 Replacement Reactions (cont.) Double replacement reactions occur when ions exchange between two compounds.Double replacement reactions This figure shows a generic double replacement equation.

Section 9-2 Replacement Reactions (cont.) The solid product produced during a chemical reaction in a solution is called a precipitate. precipitate All double replacement reactions produce either water, a precipitate, or a gas.

Section 9-2 Replacement Reactions (cont.) This table shows the steps to write double replacement reactions.

Section 9-2 Replacement Reactions (cont.) This table summarizes different ways to predict the products of a chemical reaction.

Section 9-3 Section 9.3 Reactions in Aqueous Solutions Describe aqueous solutions. solution: a uniform mixture that might contain solids, liquids, or gases Write complete ionic and net ionic equations for chemical reactions in aqueous solutions. Predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas.

Section 9-3 Section 9.3 Reactions in Aqueous Solutions (cont.) aqueous solution solute solvent Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases. complete ionic equation spectator ion net ionic equation

Section 9-3 Aqueous Solutions An aqueous solution contains one or more dissolved substances (called solutes) in water.aqueous solution solutes The solvent is the most plentiful substance in a solution.solvent

Section 9-3 Aqueous Solutions (cont.) Water is always the solvent in an aqueous solution. There are many possible solutes—sugar and alcohol are molecular compounds that exist as molecules in aqueous solutions. Compounds that produce hydrogen ions in aqueous solutions are acids.

Section 9-3 Aqueous Solutions (cont.) Ionic compounds can also be solutes in aqueous solutions. When ionic compounds dissolve in water, their ions separate in a process called dissociation.

Section 9-3 Types of Reactions in Aqueous Solutions When two solutions that contain ions as solutes are combined, the ions might react. If they react, it is always a double replacement reaction. Three products can form: precipitates, water, or gases.

Section 9-3 Types of Reactions in Aqueous Solutions (cont.) Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide. 2NaOH(aq) + CuCl 2 (aq) → 2NaCl(aq) + Cu(OH) 2 (s) Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations. complete ionic equations 2Na + (aq) + 2OH – (aq) + Cu 2+ (aq)+ 2Cl – (aq) → 2Na + (aq) + 2Cl – (aq) + Cu(OH) 2 (s)

Section 9-3 Types of Reactions in Aqueous Solutions (cont.) Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations.spectator ions Formulas that include only the particles that participate in reactions are called net ionic equations.net ionic equations 2OH – (aq) + Cu 2+ (aq) → Cu(OH) 2 (s)

Section 9-3 Types of Reactions in Aqueous Solutions (cont.) Some reactions produce more water molecules. No evidence of a chemical reaction is observable. HBr(aq) + NaOH(aq) → H 2 O(l) + NaBr(aq) Without spectator ions H + (aq) + OH – (aq) → H 2 O(l).

Section 9-3 Types of Reactions in Aqueous Solutions (cont.) Gases that are commonly produced are carbon dioxide, hydrogen cyanide, and hydrogen sulfide. 2HI(aq) + Li 2 S(aq) → H 2 S(g) + 2LiI(aq)

Section 9-3 Types of Reactions in Aqueous Solutions (cont.) Another example is mixing vinegar and baking soda, which produces carbon dioxide gas. HCl(aq) + NaHCO 3 (aq) → H 2 CO 3 (aq) + NaCl(aq) H 2 CO 3 (aq) decomposes immediately. H 2 CO 3 (aq) → H 2 O(l) + CO 2 (g)

Section 9-3 Types of Reactions in Aqueous Solutions (cont.) Two reactions can be combined and represented by a single chemical reaction.

Section 9-3 Types of Reactions in Aqueous Solutions (cont.) Reaction 1 HCl(aq) + NaHCO 3 (aq) → H 2 CO 3 (aq) + NaCl(aq) Reaction 2 H 2 CO 3 (aq) → H 2 O(l) + CO 2 (g) Combined equation HCl(aq) + NaHCO 3 (aq) + H 2 CO 3 (aq) → H 2 CO 3 (aq) + NaCl(aq) + H 2 O(l) + CO 2 (g) Overall equation HCl(aq) + NaHCO 3 (aq) → H 2 O(l) + CO 2 (g) + NaCl(aq)

Study Guide 1 Section 9.1 Reactions and Equations Key Concepts Some physical changes are evidence that indicate a chemical reaction has occurred. Word equations and skeleton equations provide important information about a chemical reaction. A chemical equation gives the identities and relative amounts of the reactants and products that are involved in a chemical reaction. Balancing an equation involves adjusting the coefficients until the number of atoms of each element is equal on both sides of the equation.

Study Guide 2 Section 9.2 Classifying Chemical Reactions Key Concepts Classifying chemical reactions makes them easier to understand, remember, and recognize. Activity series of metals and halogens can be used to predict if single-replacement reactions will occur.

Study Guide 3 Section 9.3 Reactions in Aqueous Solutions Key Concepts In aqueous solutions, the solvent is always water. There are many possible solutes. Many molecular compounds form ions when they dissolve in water. When some ionic compounds dissolve in water, their ions separate. When two aqueous solutions that contain ions as solutes are combined, the ions might react with one another. The solvent molecules do not usually react. Reactions that occur in aqueous solutions are double- replacement reactions.