Chemical Reactions and Equations

Chapter 8

Chemical reactions….• Process by which one or more substances are

• described by a

4 Signs of a Chemical Reaction:1. Evolution of _________ and

________________2. Production of ______________3. Formation of a

_____________________(solid produced as a result of a chem rxn in a sol’n)

4. _____________________change

Chemical equation• Represents the identities and relative amounts of the

reactants and products in a chemical reaction

• (NH4)2Cr2O7(s) ---> N2(g) + Cr2O3(s) + 4H2O(g)

Characteristics:– represents the _______________________________

– contains correct _________________ for the reactants & products

– satisfies the law of ____________________________ (same # and kind of atoms on both sides of the equation)

(NH4)2Cr2O7(s)---> N2(g) + Cr2O3(s) + 4H2O(g)

• Formula equation: uses symbols/formulas to represent the reactants and products

• Reactants

• products

• coefficient (understood to be “1” if no # appears

• symbols (p.246)

ammonium dichromate --> nitrogen + chromium(III) oxide + water

• Word equation: (previous ex.)

• only fulfills ONE characteristic of a chem eq

(____________________________________)

• 1st step in writing a balanced chemical equation

Steps to write a balanced chemical equation:

1. Write the word equation.

2. Convert the word equation into a formula equation.

3. Include symbols, where known.

4. Balance the equation. NEVER CHANGE A SUBCRIPT IN BALANCING EQUATIONS!

Cu + H2SO4 CuSO4 + SO2 + H2OCu

H

S

O

Cu + H2SO4 CuSO4 + SO2 + H2O

SiF4 + H2O H2SiF6 + H2SiO3

Si

F

H

O

SiF4 + H2O H2SiF6 + H2SiO3

Solutions of lead(II) nitrate and sodium hydroxide react to produce a lead(II) hydroxide precipitate and an aqueous solution of sodium nitrate.

Solid rubidium oxide reacts with water to produce an aqueous solution of rubidium

hydroxide.

Lithium reacts with a hydrochloric acid solution to produce an aqueous solution of

lithium chloride and hydrogen.

In the presence of an electrical current, sodium hydroxide can be produced from the reaction of a sodium chloride solution with water. Hydrogen and chlorine gases are the other products.

Aluminum sulfate is produced when aluminum hydroxide reacts with sulfuric acid. Water is the other product.

5 types of chemical reactions:

1. synthesis (composition)

2. decomposition

3. single-replacement (displacement)

4. double-replacement (displacement)

5. combustion

Synthesis Reactions

• 2 or more substances combine to form a new compound

• 2 H2 + O2 2H2O

Reactions of metals with oxygen and sulfur

• magnesium metal + oxygen

• barium + sulfur (S8)

Some metals can form oxides of varying oxidation #:

• iron + oxygen iron(II) oxide

• iron + oxygen iron(III) oxide

Nonmetals can also form oxides

• S8(s) + 8O2(g) 8SO2(g)

• C(s) + O2(g) CO2(g)

• 2C(s) + O2(g) 2CO(g)

Reactions of metals with halogens• potassium + iodine

• strontium + bromine

• cobalt + fluorine [cobalt(III) ion forms]

Synthesis reactions with metal oxides

• active metals* oxides + water hydroxides

• calcium oxide + water

• *(see p. 266)

Synthesis reactions with nonmetal oxides

• nonmetal oxides + water oxyacids

• sulfur dioxide + water

Synthesis reaction of metal oxide & nonmetal oxide

• calcium oxide + sulfur dioxide

Decomposition

• a single cmpd undergoes a rxn that produces 2 or more simpler substances

•H2CO3 H2O + CO2

Decomposition of…

• binary cmpds

• metal carbonates

• metal hydroxide

• metal chlorates

• acid

Decomposition of binary cmpds

• simplest decomposition rxn

• decomposition into elements

• ELECTROLYSIS: decomp by an electric current

• 2 H2O(l) electricity--->

Decomposition of Metal Carbonates

• when heated (∆), produce a metal oxide and carbon dioxide gas

• CaCO3(s) -∆

Decomposition of Metal Hydroxides

• all metals except Gp 1 decomp when heated to produce metal oxides and water

• Ca(OH)2(s) -∆ CaO(s) + H2O(g)

Decomposition of Metal Chlorates

• when heated, decompose to produce a metal chloride and oxygen

• KClO3(s) -∆ 2KCl(s) + 3O2(g)

Decomposition of Acids

• Many acids decompose into nonmetal oxides and water

• H2SO4(aq) -∆

• H2CO3(aq)

Single Replacement Reaction

• one element replaces a similar element in a cmpd

• 2 Al + Fe2O3 Al2O3 + 2 Fe

Single Replacement Reaction of…

• a metal in a cmpd by another metal

• hydrogen in water by a metal

• hydrogen in an acid by a metal

• replacement of halogens

Replacement of a metal in a cmpd by another metal

• aluminum + lead(II) nitrate

• (p. 266 Al is more reactive than Pb so a spontaneous reaction will occur)

Replacement of H in water by a metal (active)

very active metals (i.e. Gp 1) pulls one H from the water

• sodium + water

Replacement of H in water by a metal (less-active)

less- active metals reacts with steam and pulls-off both hydrogens from the water

• iron + water

Replacement of H in an acid by a metal

more-active metals reacts with some acidic soln’s

• magnesium + hydrochloric acid

Replacement of Halogens• a more reactive halogen will replace a

less-active halogen

• the higher up in the Gp 17 family, the MORE reactive the halogen

• Reactivity: F>Cl>Br>I

• chlorine gas + potassium bromide sol’n

• fluorine gas + sodium chloride sol’n

• bromine liquid + potassium chloride sol’n

Double replacement reactions

• ions of 2 cmpds exchange places in an aqueous solution to form 2 new cmpds

• ZnBr2 + 2 AgNO3 Zn(NO3)2 + 2 AgBr

Double displacement reactions…..

• formation of a precipitate

• formation of a gas

• formation of water

Formation of a precipitate

• one product is insoluble (or just slightly soluble) …see page 427

• potassium iodide + lead (II) nitrate

Formation of a gas• one product is an insoluble gas and bubbles

out

• iron(II) sulfide + hydrochloric acid sol’n

Formation of Water

• one of the products yields the molecular cmpd water

• hydrochloric acid + sodium hydroxide

Combustion Reactions

• substance reacts with oxygen and releases a large amount of energy (light and heat)

• hydrogen + oxygen water vapor

• hydrocarbon + oxygen carbon dioxide + water

• Combustion (burning) of propane:

• C3H8(g) + O2

Will cobalt react with sodium chloride?

Co(s) + NaCl(aq) ?

Activity Series

• list of elements organized according to the ease with which the elements undergo certain chemical reactions

• are

at the TOP and can replace a metal in a cmpd found below it in single displacement reactions

water

X

steam

X

acid

X

oxygen

X

X X X

X X

X

Will the following react? IF so, write an equation.

• Mn + H2O --30C ?

• Cd + O2

• Ag + HCl

Will the following react? Write an equation if it does.

• Br2 and HCl

• Cl2 and KI