Chemical reactions

Chapter 10

Add ionic/net ionic equationsAdd activity series (metals/nonmetals)

Chemical changesChemical change results in formation of

a new substanceChemical bonds are made and brokenEnergy changes:

Breaking bonds absorbs energyMaking bonds releases energyOverall energy change may be + or -

Signs of a chemical reaction

Certain physical changes can indicate the occurrence of chemical changes:

Color change Precipitate: sudden formation of a solid from a

liquid solution Formation of a gas (fizzing) Change in temperature (evolution or

absorption of heat) Flame or explosion

Chemical equationsReactants produce Products

A + B C + DReactants Products

Word equationssodium + chlorine sodium chloride

“Skeleton” equations (unbalanced)Na + Cl2 NaCl

Chemical equationsBalanced chemical equations: required

by the law of conservation of matterNa + Cl2 NaCl

Formulas may not be changedCoefficients are used to equalize the

number of atoms on both sides of the equation

Balancing chemical equations

Count atomsNa + Cl2 NaCl

Left side: 1 Na, 2ClRight side: 1 Na, 1 ClAdd coefficients to balance equation

2Na + Cl2 2NaClRecount atoms to double check

Balancing chemical equations

KOH + Co(NO3)3 KNO3 + Co(OH)3

If polyatomic ions are unchanged, they can be counted as a unit

Left side: 1 K, 1 OH, 1 Co, 3NO3

Right side: 1 K, 3 OH, 1 Co, 1 NO3

Fix hydroxides3KOH + Co(NO3)3 KNO3 + Co(OH)3

Balancing chemical equations

Fix nitrates3KOH + Co(NO3)3 3KNO3 + Co(OH)3

Al2(CO3)3 Al2O3 + CO2

Count atoms: Left side: 2 Al, 3 C, 9 ORight side: 2 Al, 1 C, 5 O

Fix carbons

Balancing chemical equations

Al2(CO3)3 Al2O3 + 3CO2This fixes the oxygens also

CH4 + O2 CO2 + H2O 1C 4H 2O 1C 2H 3OIn combustion reactions always leave

the oxygen until the lastFix hydrogens

CH4 + O2 CO2 + 2H2O

Balancing chemical equations

Fix oxygensCH4 + 2O2 CO2 + 2H2O

Burning even numbered alkanesC2H6 + O2 CO2 + H2O

Fix carbonsC2H6 + O2 2CO2 + H2O

Fix hydrogens

Balancing chemical equations

C2H6 + O2 2CO2 + 3H2OUse fraction for oxygens

C2H6 + 3.5O2 2CO2 + 3H2ODouble all coefficients to remove fraction

2C2H6 + 7O2 4CO2 + 6H2O

Symbols for physical state

Symbols for physical state(s) = solid(l) = liquid(g) = gas

(aq) = aqueous (dissolved in water)HC2H3O2(aq)+ NaHCO3(s)NaC2H3O2(aq)+ CO2(g)

+H2O(l)

Types of Chemical ReactionsSynthesis reaction

A + B CC + O2 CO2

2Na + Cl2 2NaClNa + Cl2 NaCl

Types of Chemical ReactionsDecomposition

C A + BH2O H2 + O2

KClO3 KCl + O22KClO3 2KCl + 3O2

(NH4)2Cr2O7N2+4H2O+Cr2O3

22

Types of Chemical ReactionsSingle displacement

A + BC AC + BMetals displace metals, nonmetals

displace nonmetals

Fe + CuSO4Cu + FeSO4

Cl2+2NaBr(aq)Br2+2NaCl(aq)Cl2+NaBr(aq)Br2+NaCl(aq)

Types of Chemical ReactionsDouble displacement

AB + CD AD + CBMetals and nonmetals switch partners

NaCl+AgNO3NaNO3+AgCl(s)

2KI + Pb(NO3)2PbI2 + 2KNO3 KI+Pb(NO3)2PbI2(s)+KNO3

Types of Chemical ReactionsCombustion Element or compound reacting with

oxygen

2Mg + O2 2MgO

2H2 + O2 2H2O

Combustion ReactionsCarbon containing compounds give CO2

and water

   

CH4 + O2 CO2 + H2OCH4 + 2O2CO2+ 2H2O

C2H5OH+O2CO2+H2O C2H5OH+3O22CO2+3H2O