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Chemical Reactions. Section 9.1 Reactions and Equations Section 9.2 Classifying Chemical Reactions Section 9.3 Reactions in Aqueous Solutions. Click a hyperlink or folder tab to view the corresponding slides. Exit. Chapter Menu. Section 9.1 Reactions and Equations. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter Menu
Chemical Reactions
Section 9.1 Reactions and Equations
Section 9.2 Classifying Chemical Reactions
Section 9.3 Reactions in Aqueous Solutions
ExitClick a hyperlink or folder tab to view
the corresponding slides.
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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.
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Section 9-1
Chemical Reactions
• The process by which one or more substances are rearranged to form different substances is called a chemical reaction.
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Section 9-1
Chemical Reactions (cont.)
• Evidence of a chemical reaction
– Change in temperature
– Change in color
– Odor, gas, or bubbles may form.
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Section 9-1
Representing Chemical Reactions
• Chemists use statements called equations to represent chemical reactions.
• Reactants are the starting substances.
• Products are the substances formed in the reaction.
• This table summarizes the symbols used in chemical equations.
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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) → AlBr3(s)
• Skeleton equations lack information about how many atoms are involved in the reaction.
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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.
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Section 9-1
Balancing Chemical Equations
• This figure shows the balanced equation for the reaction between aluminum and bromine.
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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.
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Section 9-1
Balancing Chemical Equations (cont.)
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Section 9-1
Balancing Chemical Equations (cont.)
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Section 9-1
Balancing Chemical Equations (cont.)
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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.
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Section 9-1
Balancing Chemical Equations (cont.)
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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.
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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
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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.
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Section 9-2
Types of Chemical Reactions (cont.)
• When two elements react, the reaction is always a synthesis reaction.
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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.
• Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.
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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 reactions often require an energy source, such as heat, light, or electricity, to occur.
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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.
A + BX → AX + B
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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.
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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.
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Section 9-2
Replacement Reactions (cont.)
• Double replacement reactions occur when ions exchange between two compounds.
• This figure shows a generic double replacement equation.
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Section 9-2
Replacement Reactions (cont.)
• The solid product produced during a chemical reaction in a solution is called a precipitate.
• All double replacement reactions produce either water, a precipitate, or a gas.
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Section 9-2
Replacement Reactions (cont.)
• This table shows the steps to write double replacement reactions.
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Section 9-2
Replacement Reactions (cont.)
• This table summarizes different ways to predict the products of a chemical reaction.
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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.
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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
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Section 9-3
Aqueous Solutions
• An aqueous solution contains one or more dissolved substances (called solutes) in water.
• The solvent is the most plentiful substance in a solution.
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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.
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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.
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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.
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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) + CuCl2(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.
2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+
(aq) + 2Cl–(aq) + Cu(OH)2(s)
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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.
• Formulas that include only the particles that participate in reactions are called net ionic equations.
2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)
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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) → H2O(l) + NaBr(aq)
• Without spectator ions H+(aq) + OH–(aq) → H2O(l).
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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) + Li2S(aq) → H2S(g) + 2LiI(aq)
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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) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)
• H2CO3(aq) decomposes immediately.
H2CO3(aq) → H2O(l) + CO2(g)
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Section 9-3
Types of Reactions in Aqueous Solutions (cont.)
• Two reactions can be combined and represented by a single chemical reaction.
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Section 9-3
Types of Reactions in Aqueous Solutions (cont.)
Reaction 1
HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)
Reaction 2
H2CO3(aq) → H2O(l) + CO2(g)
Combined equation
HCl(aq) + NaHCO3(aq) + H2CO3(aq) → H2CO3(aq) + NaCl(aq) + H2O(l) + CO2(g)
Overall equation
HCl(aq) + NaHCO3(aq) → H2O(l) + CO2(g) + NaCl(aq)
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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.
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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.
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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.