Chapter 8 Chemical Equations and Reactions Chemical Equations and Reactions

8-1 Describing Chemical Reactions Chemical reaction – process by which one or more substances are changed into one or more different substances Chemical reaction – process by which one or more substances are changed into one or more different substances Reactants – starting substances Reactants – starting substances Products – ending substances Products – ending substances Conservation of mass tells us that the mass of the reactants must be equal to the mass of the products Conservation of mass tells us that the mass of the reactants must be equal to the mass of the products

8-1 Chemical Equations Chemical equation – represents (with symbols and formulas) the identities and relative amounts of the reactants and products in a chemical reaction Chemical equation – represents (with symbols and formulas) the identities and relative amounts of the reactants and products in a chemical reaction

8-1 Signs of a Chemical Reaction Evolution of heat and light Evolution of heat and light Production of a gas/bubbles Production of a gas/bubbles Formation of a precipitate Formation of a precipitate Color change Color change

8-1 Requirements for Properly Written Chemical Equations All reactants and products must be represented All reactants and products must be represented Correct symbols and formulas must be used for all substances in the equation (remember diatomics!) Correct symbols and formulas must be used for all substances in the equation (remember diatomics!) Reactants on left, products on right Reactants on left, products on right Arrow means “yields” or “forms” Arrow means “yields” or “forms” Law of conservation of matter must be satisfied – equations must be BALANCED Law of conservation of matter must be satisfied – equations must be BALANCED

8-1 Balancing Chemical Equations Equations must be balanced to show the same number of atoms of each type on both sides of the equation Equations must be balanced to show the same number of atoms of each type on both sides of the equation Balance equations by writing coefficients Balance equations by writing coefficients Coefficient – a small whole number that appears in front of a formula in a chemical equation Coefficient – a small whole number that appears in front of a formula in a chemical equation NEVER change subscripts! NEVER change subscripts!

8-1 Balancing Equations Write a balanced chemical equation for the formation of ammonia from its elements.

8-1 Balancing Chemical Equations Write a balanced chemical equation for the decomposition of sodium chloride to its elements.

8-1 Word and Formula Equations It is often helpful to begin by writing a word equation that represents all the facts about a chemical reaction. It is often helpful to begin by writing a word equation that represents all the facts about a chemical reaction. In a word equation, reactants and products are represented by words. In a word equation, reactants and products are represented by words. methane + oxygen  carbon dioxide + water

8-1 Word and Formula Equations A formula equation represents the reactants and products of a chemical reaction by their symbols or formulas. A formula equation represents the reactants and products of a chemical reaction by their symbols or formulas. CH 4 + O 2  CO 2 + H 2 O (unbalanced)

8-1 Additional Symbols Used in Chemical Equations (s)(l)(aq)(g)YieldsSolidLiquidAqueousgas

8-1 Reversible Reactions A reversible reaction is one in which products can re-form the original reactants 3Fe(s) + 4H 2 O(g) Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(g) Fe 3 O 4 (s) + 4H 2 (g)

8-1 Reactions Requiring Heat Some reactions will only proceed if the reactants are heated. Some reactions will only proceed if the reactants are heated. 2HgO(s)  2Hg(l) + O 2 (g) 2HgO(s)  2Hg(l) + O 2 (g)

8-1 Practice Translate the following into a sentence: 2NaOH(aq) + MgCl 2 (aq)  2NaCl(aq) + Mg(OH) 2 (s) 2NaOH(aq) + MgCl 2 (aq)  2NaCl(aq) + Mg(OH) 2 (s) NaCl(aq) + AgNO 3 (aq)  NaNO 3 (aq) + AgCl(s) NaCl(aq) + AgNO 3 (aq)  NaNO 3 (aq) + AgCl(s)

8-1 Practice Write a balanced chemical equation for the following processes: Solid calcium reacts with solid sulfur to produce solid calcium sulfide. Hydrogen gas reacts with fluorine gas to produce hydrogen fluoride gas.

8-2 Types of Chemical Reactions Using generalizations about the ways various substances interact with each other, we can predict the products of reactions Using generalizations about the ways various substances interact with each other, we can predict the products of reactions There are five main types of chemical reactions. There are five main types of chemical reactions.

8-2 Types of Chemical Reactions Synthesis Synthesis Decomposition Decomposition Single replacement Single replacement Double replacement Double replacement Combustion (of hydrocarbons) Combustion (of hydrocarbons)

8-2 Synthesis Reactions Two or more substances react to form one new compound Two or more substances react to form one new compound A + X  AX Recognize by SINGLE PRODUCT

8-2 Synthesis Reactions Reactions of elements with oxygen or sulfur FORM OXIDES OR SULFIDES Reactions of elements with oxygen or sulfur FORM OXIDES OR SULFIDES Magnesium reacts with oxygen Magnesium reacts with oxygen Barium reacts with sulfur Barium reacts with sulfur Rubidium reacts with sulfur Rubidium reacts with sulfur

8-2 Synthesis Reactions Reactions of metals with halogens FORM METAL HALIDES Reactions of metals with halogens FORM METAL HALIDES Sodium reacts with chlorine Sodium reacts with chlorine Potassium reacts with iodine Potassium reacts with iodine Magnesium reacts with fluorine Magnesium reacts with fluorine

8-2 Synthesis Reactions Metal oxides react with water to form metal hydroxides Metal oxides react with water to form metal hydroxides Calcium oxide reacts with water Calcium oxide reacts with water Magnesium oxide reacts with water Magnesium oxide reacts with water

8-2 Synthesis Reactions Nonmetal oxides react with water to form acids Nonmetal oxides react with water to form acids Sulfur dioxide reacts with water Sulfur dioxide reacts with water Carbon dioxide reacts with water Carbon dioxide reacts with water

8-2 Decomposition Reactions A single compound breaks down to produce two or more simpler substances A single compound breaks down to produce two or more simpler substances AX  A + X Recognize by single reactant Often require energy in the form of heat, light or electricity.

8-2 Decomposition Reactions Decomposition of binary compounds produces elements Decomposition of binary compounds produces elements Decomposition of water Decomposition of water Decomposition of sodium chloride Decomposition of sodium chloride Decomposition of magnesium mercury (II) oxide Decomposition of magnesium mercury (II) oxide

8-2 Decomposition Reactions Decomposition of metal carbonates FORMS METAL OXIDE AND CARBON DIOXIDE Decomposition of metal carbonates FORMS METAL OXIDE AND CARBON DIOXIDE Decomposition of calcium carbonate Decomposition of calcium carbonate Decomposition of magnesium carbonate Decomposition of magnesium carbonate

8-2 Decomposition Reactions Decomposition of metal hydroxides FORMS METAL OXIDES AND WATER Decomposition of metal hydroxides FORMS METAL OXIDES AND WATER Decomposition of calcium hydroxide Decomposition of calcium hydroxide Decomposition of copper (II) hydroxide Decomposition of copper (II) hydroxide

8-2 Decomposition Reactions Decomposition of metal chlorates FORMS METAL CHLORIDES AND OXYGEN Decomposition of metal chlorates FORMS METAL CHLORIDES AND OXYGEN Decomposition of potassium chlorate Decomposition of potassium chlorate Decomposition of sodium chlorate Decomposition of sodium chlorate

8-2 Decomposition Reactions Decomposition of acids PRODUCES NONMETAL OXIDES AND WATER Decomposition of acids PRODUCES NONMETAL OXIDES AND WATER Decomposition of carbonic acid Decomposition of carbonic acid Decomposition of sulfuric acid Decomposition of sulfuric acid

8-2 Single Replacement Reactions One element replaces another similar element in a compound One element replaces another similar element in a compound A + BX  AX + B OR Y + BX  BY + X

8-2 Single Replacement Reactions Replacement of a metal by another metal Replacement of a metal by another metal Aluminum reacts with lead nitrate Aluminum reacts with lead nitrate Sodium reacts with iron (II) chloride Sodium reacts with iron (II) chloride Calcium reacts with aluminum phosphate Calcium reacts with aluminum phosphate

8-2 Single Replacement Reactions Replacement of hydrogen by a metal Replacement of hydrogen by a metal Sodium reacts with water Sodium reacts with water Magnesium reacts with hydrochloric acid Magnesium reacts with hydrochloric acid Calcium reacts with nitric acid Calcium reacts with nitric acid

8-2 Single Replacement Reactions Replacement of Halogens Replacement of Halogens Chlorine reacts with potassium bromide Chlorine reacts with potassium bromide Fluorine reacts with sodium chloride Fluorine reacts with sodium chloride Fluorine reacts with potassium iodide Fluorine reacts with potassium iodide

8-3 Activity Series of the Elements An activity series is a list of elements organized according to the ease with which the elements undergo certain chemical reactions An activity series is a list of elements organized according to the ease with which the elements undergo certain chemical reactions For metals, greater activity means greater ease of LOSS OF ELECTRONS to form cations. For metals, greater activity means greater ease of LOSS OF ELECTRONS to form cations. For nonmetals, greater activity means greater ease of GAIN OF ELECTRONS to form anions. For nonmetals, greater activity means greater ease of GAIN OF ELECTRONS to form anions. An activity series can be used to determine whether or not a single replacement reaction will take place. An activity series can be used to determine whether or not a single replacement reaction will take place.

8-3 Activity Series More active metals are HIGHER on the list. More active metals are HIGHER on the list. A more active metal can replace a less active metal on the activity series. A more active metal can replace a less active metal on the activity series. Example: Na + CoCl 2  Example: Na + CoCl 2  Example: Cu + AlCl 3  Example: Cu + AlCl 3  Example: Cr + HCl  Example: Cr + HCl  Example: Au + MgSO 4  Example: Au + MgSO 4 

8-3 Activity Series Example: Cl 2 + NaBr  Example: Cl 2 + NaBr  Example: Br 2 + KF  Example: Br 2 + KF  Example: Cl 2 + MgBr 2  Example: Cl 2 + MgBr 2 

8-2 Double Replacement Reactions The ions of two compounds exchange places to form two new compounds The ions of two compounds exchange places to form two new compounds One of the products is usually a precipitate, gas or molecular compound (like water) One of the products is usually a precipitate, gas or molecular compound (like water) AX + BY  AY + BX

8-2 Double Replacement Reactions Formation of a precipitate Formation of a precipitate Potassium iodide reacts with lead (II) nitrate Potassium iodide reacts with lead (II) nitrate Magnesium chloride reacts with sodium hydroxide Magnesium chloride reacts with sodium hydroxide

8-2 Double Replacement Reactions Formation of a gas Formation of a gas Iron (II) sulfide reacts with hydrochloric acid Iron (II) sulfide reacts with hydrochloric acid

8-2 Double Replacement Reactions Formation of water Formation of water An acid reacts with a base – also called a NEUTRALIZATION reaction An acid reacts with a base – also called a NEUTRALIZATION reaction Hydrochloric acid reacts with sodium hydroxide Hydrochloric acid reacts with sodium hydroxide Sulfuric acid reacts with potassium hydroxide Sulfuric acid reacts with potassium hydroxide

8-2 Combustion Reactions A substance combines with oxygen, releasing a large amount of energy in the form of light and heat A substance combines with oxygen, releasing a large amount of energy in the form of light and heat Hydrocarbons burn in oxygen Hydrocarbons burn in oxygen A hydrocarbon is a compound composed of hydrogen and carbon A hydrocarbon is a compound composed of hydrogen and carbon

8-2 Combustion Reactions Combustion of hydrocarbons Combustion of hydrocarbons When a hydrocarbon reacts with oxygen, the products are carbon dioxide and water When a hydrocarbon reacts with oxygen, the products are carbon dioxide and water Combustion of butane Combustion of butane Combustion of heptane Combustion of heptane

8-2 Simple Hydrocarbons (C n H 2n+2 ) CH 4 CH 4 C 2 H 6 C 2 H 6 C 3 H 8 C 3 H 8 C 4 H 10 C 4 H 10 C 5 H 12 C 5 H 12 C 6 H 14 C 6 H 14 C 7 H 16 C 7 H 16 C 8 H 18 C 8 H 18 C 9 H 20 C 9 H 20 C 10 H 22 C 10 H 22 methane methane ethane ethane propane propane butane butane pentane pentane hexane hexane heptane heptane octane octane nonane nonane decane decane

It’s over!