Chapter 10Chapter 10

Chemical ReactionsChemical Reactions

Chemical ReactionsChemical Reactions

The process by which atoms of one or The process by which atoms of one or more substances are rearranged to form more substances are rearranged to form different substances is called a different substances is called a chemical chemical reaction.reaction.

Some ways to know that a chemical Some ways to know that a chemical reaction has occurred include absorption reaction has occurred include absorption of heat and release of energy in the form of heat and release of energy in the form of light or heat, color change, production of light or heat, color change, production of a gas, and the appearance of gas of a gas, and the appearance of gas bubbles or a solid.bubbles or a solid.

Chemical EquationsChemical Equations

Statements called equations are used Statements called equations are used to represent chemical reactions. to represent chemical reactions.

ReactantsReactants, or starting substances, and , or starting substances, and the the productsproducts, or substances formed , or substances formed during a reaction, are shown in a during a reaction, are shown in a chemical reaction.chemical reaction.

The arrow in the reaction means The arrow in the reaction means “yields”.“yields”.

Plus signs separate different reactants Plus signs separate different reactants and products.and products.

ExamplesExamples

REACTANT + REACTANTREACTANT + REACTANT

““yields”yields”

PRODUCT + PRODUCTPRODUCT + PRODUCT

State SymbolsState Symbols

Sometimes state symbols will be Sometimes state symbols will be used to indicate the state of matter used to indicate the state of matter in the reaction.in the reaction.– (s) Solid(s) Solid– (l) Liquid(l) Liquid– (g) Gas(g) Gas– (aq) Aqueous [Water solution](aq) Aqueous [Water solution]

EquationsEquations

Equations can be written in words, in Equations can be written in words, in which the reactants and products are which the reactants and products are indicated by their names.indicated by their names.

Word equations can be replaced by Word equations can be replaced by skeleton equations which use skeleton equations which use chemical formulas rather than words.chemical formulas rather than words.

Skeleton equations are more Skeleton equations are more informative because they identify the informative because they identify the atoms that make up each reactant atoms that make up each reactant and product.and product.

ExampleExample

Write a word equation and skeleton Write a word equation and skeleton equation for the reaction in which equation for the reaction in which hydrogen gas reacts with oxygen gas hydrogen gas reacts with oxygen gas to form liquid water.to form liquid water.

hydrogen(g) + Oxygen(g) hydrogen(g) + Oxygen(g) Water (l)Water (l)

HH22 (g) + O (g) + O22 (g) (g) HH22O (l)O (l)

PracticePractice

Write a word equation and a skeleton Write a word equation and a skeleton equation for each of the following equation for each of the following descriptions of chemical reactions.descriptions of chemical reactions.– Solid lithium reacts with chlorine gas to Solid lithium reacts with chlorine gas to

produce solid lithium chloride.produce solid lithium chloride.– Nitrogen gas reacts with oxygen gas to Nitrogen gas reacts with oxygen gas to

produce nitrogen dioxide gas.produce nitrogen dioxide gas.– Solid iron reacts with aqueous copper Solid iron reacts with aqueous copper

(II) nitrate to produce solid copper and (II) nitrate to produce solid copper and aqueous iron (II) nitrate.aqueous iron (II) nitrate.

Balanced Chemical Balanced Chemical EquationsEquations

Skeleton equations do not reflect the fact Skeleton equations do not reflect the fact that matter is conserved during a reaction.that matter is conserved during a reaction.

An equation must reflect that the same An equation must reflect that the same number of each kind of atom on both sides number of each kind of atom on both sides of the arrow. This is called a of the arrow. This is called a balanced balanced chemical equation.chemical equation.

To balance a chemical equation, use To balance a chemical equation, use coefficientscoefficients, numbers placed in front of , numbers placed in front of the compound. When no coefficient the compound. When no coefficient appears, the number is understood to be 1.appears, the number is understood to be 1.

ProcedureProcedure

1.1. Write the skeleton equation.Write the skeleton equation.2.2. Count the atoms of the elements in the Count the atoms of the elements in the

reactants. Polyatomic atoms that remain reactants. Polyatomic atoms that remain unchanged can be counted as elements.unchanged can be counted as elements.

3.3. Count the atoms of the elements in the Count the atoms of the elements in the products.products.

4.4. Change coefficients to make numbers Change coefficients to make numbers equal. DO NOT CHANGE SUBSCRIPTS.equal. DO NOT CHANGE SUBSCRIPTS.

5.5. Write coefficients in their lowest possible Write coefficients in their lowest possible ratios.ratios.

6.6. Check your work.Check your work.

Classifying Chemical Classifying Chemical ReactionsReactions

Types of ReactionsTypes of Reactions

There are five basic types of There are five basic types of chemical reactions.chemical reactions.

The first of these types is the The first of these types is the SynthesisSynthesis reaction. reaction.

In the synthesis reaction, there are In the synthesis reaction, there are more than one reactants and only more than one reactants and only one product. Synthesis means one product. Synthesis means combine.combine.

Combustion ReactionsCombustion Reactions

A combustion reaction is a reaction A combustion reaction is a reaction that has as one reactant oxygen gas. that has as one reactant oxygen gas.

Combustion reactions produce lots of Combustion reactions produce lots of heat and light and the product is heat and light and the product is usually usually carbon dioxide and water.carbon dioxide and water.

CHCH4 4 (g)+ 2O(g)+ 2O22 (g) CO (g) CO22 (g) + 2H (g) + 2H22O O (g) (g)

DecompositionDecomposition

A decomposition reaction is one A decomposition reaction is one where a single compound breaks where a single compound breaks down into two or more elements or down into two or more elements or new compounds.new compounds.

2Al2Al22OO33 4 Al + 3O 4 Al + 3O22

Single-Replacement Single-Replacement ReactionsReactions

In a single-replacement reaction, In a single-replacement reaction, atoms of an element replace the atoms of an element replace the atoms of another element in a atoms of another element in a compound.compound.

For example, in the replacement of For example, in the replacement of silver in silver nitrate by zinc metal.silver in silver nitrate by zinc metal.

Zn (s) + 2AgNOZn (s) + 2AgNO33 (aq) Zn(NO (aq) Zn(NO33))22 (aq) + 2 Ag (aq) + 2 Ag (s)(s)

Activity SeriesActivity Series

Not all metals will replace one Not all metals will replace one another. Only a metal that is more another. Only a metal that is more chemically reactive will replace one chemically reactive will replace one that is less reactive.that is less reactive.

The order of such reactivity is called The order of such reactivity is called an activity series and you have a an activity series and you have a copy of one in your reference tables.copy of one in your reference tables.

ReactivityReactivity

Any metal in an activity series will Any metal in an activity series will replace the metals below it in their replace the metals below it in their compounds.compounds.

With elemental halogens, one replaces With elemental halogens, one replaces the other if the second lies below it in the other if the second lies below it in the periodic table.the periodic table.

Fluorine is more reactive than, chlorine, Fluorine is more reactive than, chlorine, which is more active than bromine, which is more active than bromine, which is more active than iodine.which is more active than iodine.

ExampleExample

Use an activity series to predict the Use an activity series to predict the single-replacement reaction that will single-replacement reaction that will occur between aluminum metal and occur between aluminum metal and lead (II) nitrate (Pb(NOlead (II) nitrate (Pb(NO33))22) in a water ) in a water solution and write its balanced solution and write its balanced chemical equation.chemical equation.

Answer:Answer:2Al (s) + 3Pb(NO2Al (s) + 3Pb(NO33))22 (aq) 2Al(NO (aq) 2Al(NO33))33 (aq) + 3 (aq) + 3

Pb(s)Pb(s)

PracticePractice Predict whether a single-replacement Predict whether a single-replacement

reaction will occur between the following reaction will occur between the following pairs of possible reactants. If so, write the pairs of possible reactants. If so, write the balanced chemical equation for the balanced chemical equation for the reaction.reaction.

1.1. Chlorine gas and aqueous potassium iodideChlorine gas and aqueous potassium iodide2.2. Magnesium metal and aqueous copper (II) Magnesium metal and aqueous copper (II)

sulfatesulfate3.3. Copper metal and iron (III) chloride in water Copper metal and iron (III) chloride in water

solutionsolution4.4. Lead metal and aqueous silver nitrateLead metal and aqueous silver nitrate

Double Replacement Double Replacement ReactionsReactions

In this reaction type, there is an exchange In this reaction type, there is an exchange of the positive ions between two of the positive ions between two compounds, often in water solutions.compounds, often in water solutions.

Often a solid, of low solubility is produced Often a solid, of low solubility is produced during the reaction and settles out of the during the reaction and settles out of the solution. This solid is called a solution. This solid is called a precipitateprecipitate..

For example,For example,Pb(NOPb(NO33))22 (aq) + 2NaCl (aq) 2NaNO (aq) + 2NaCl (aq) 2NaNO33 (aq) +PbCl (aq) +PbCl22

(s)(s)

PracticePractice Write a balanced chemical equation for each of Write a balanced chemical equation for each of

the following double-replacement reactions.the following double-replacement reactions.1.1. A water solution of sinc bromide (ZnBrA water solution of sinc bromide (ZnBr22) and a ) and a

water solution of potassium hydroxide form a water solution of potassium hydroxide form a water solution of potassium bromide and a water solution of potassium bromide and a precipitate of zinc hydroxide.precipitate of zinc hydroxide.

2.2. A water solution of copper (II) sulfate and a A water solution of copper (II) sulfate and a water solution of barium chloride produce a water solution of barium chloride produce a water solution of copper (II) chloride and solid water solution of copper (II) chloride and solid barium sulfate.barium sulfate.

3.3. A precipitate of iron (III) carbonate and a water A precipitate of iron (III) carbonate and a water solution of sodium nitrate are formed when a solution of sodium nitrate are formed when a water solution of iron (III) nitrate and a water water solution of iron (III) nitrate and a water solution of sodium carbonate are mixed.solution of sodium carbonate are mixed.

Reactions in Aqueous Reactions in Aqueous SolutionsSolutions

SolutionsSolutions

When a substance dissolves in water, When a substance dissolves in water, a solution forms. a solution forms.

A solution is a homogeneous mixture A solution is a homogeneous mixture because it has a constant because it has a constant composition throughout.composition throughout.

A solution contains one or more A solution contains one or more substances called substances called solutessolutes dissolved dissolved in the solvent.in the solvent.

Solutions (cont’d)Solutions (cont’d)

The The solventsolvent is the most plentiful is the most plentiful substance in the solution.substance in the solution.

An An aqueous solutionaqueous solution is a solution in is a solution in which the solvent is water.which the solvent is water.

When dissolved to form aqueous When dissolved to form aqueous solutions, the ions of ionic solutions, the ions of ionic compounds separate.compounds separate.

Ionic EquationsIonic Equations

To show all of the particles in solution as To show all of the particles in solution as they really exist, a they really exist, a complete ionic complete ionic equationequation can be written. can be written.

NaNa++ (aq) + Cl (aq) + Cl-- (aq) + Ag (aq) + Ag++ (aq) + NO3 (aq) + NO3-- (aq) (aq)

NaNa++ (aq)+ NO (aq)+ NO33-- (aq) + AgCl (s) (aq) + AgCl (s)

Notice that the sodium and nitrate ions Notice that the sodium and nitrate ions are present on both sides of the are present on both sides of the equation. Such ions that do not equation. Such ions that do not participate in the reaction are called participate in the reaction are called spectator ionsspectator ions..

Net Ionic EquationsNet Ionic Equations

An ionic equation that does not show An ionic equation that does not show spectator ions but only the particles spectator ions but only the particles that participate in the reaction is that participate in the reaction is called a called a net ionic equationnet ionic equation..

ExampleExample

Write the balanced chemical Write the balanced chemical equation for the reaction between equation for the reaction between aqueous solutions of strontium aqueous solutions of strontium nitrate and potassium sulfate, which nitrate and potassium sulfate, which forms the precipitate strontium forms the precipitate strontium sulfate. Then write the complete sulfate. Then write the complete ionic and net ionic equations.ionic and net ionic equations.

PracticePractice

Write the balanced chemical, complete Write the balanced chemical, complete ionic and net ionic equations for each of ionic and net ionic equations for each of the following reactions.the following reactions.

1.1. Aqueous solutions of lead (II) nitrate and Aqueous solutions of lead (II) nitrate and ammonium chloride are mixed, forming ammonium chloride are mixed, forming a precipitate of lead (II) chloride.a precipitate of lead (II) chloride.

2.2. Aqueous solutions of aluminum chloride Aqueous solutions of aluminum chloride and sodium carbonate are combined, and sodium carbonate are combined, producing solid aluminum carbonate.producing solid aluminum carbonate.

Production of Water or a Production of Water or a GasGas

Some double-displacement reactions Some double-displacement reactions in aqueous solution produce water or in aqueous solution produce water or a gas (or both) rather than a a gas (or both) rather than a precipitate.precipitate.

When this happens, show the water When this happens, show the water or gas as a product in the net ionic or gas as a product in the net ionic equation. DO NOT IONIZE!!!equation. DO NOT IONIZE!!!

ExampleExample

When hydrochloric acid and When hydrochloric acid and potassium hydroxide solutions are potassium hydroxide solutions are mixed, water results, together with mixed, water results, together with an aqueous solution of potassium an aqueous solution of potassium chloride. Write the balanced chloride. Write the balanced chemical equation, a complete ionic chemical equation, a complete ionic equation and a net ionic equation for equation and a net ionic equation for this reaction.this reaction.

PracticePractice

Write the balanced chemical, complete Write the balanced chemical, complete ionic and net ionic equations for the ionic and net ionic equations for the reactions between the following reactions between the following substances, which produce water.substances, which produce water.

1.1. Nitric acid (HNONitric acid (HNO33) and aqueous barium ) and aqueous barium hydroxidehydroxide

2.2. Sulfuric acid (HSulfuric acid (H22SOSO44) and aqueous sodium ) and aqueous sodium hydroxidehydroxide

3.3. Phosphoric acid (HPhosphoric acid (H33POPO44) and aqueous ) and aqueous lithium hydroxidelithium hydroxide

Lab TomorrowLab Tomorrow