Types of Reactions
Types of Reactions
(1) Single displacement - a reaction in which one element displaces another in a compound.
M1 + MNm ---à M + M1Nm
Nm1 + MNm --à Nm + MNm1
element + compound ---à element + compound
The element, which displaces another in a compound, must be more active (reactive) than the one it is replacing.
In order to determine if the reaction will take place, you must consult an activity series.
There are separate lists for metals and nonmetals.
Examples:
Cl2 + 2 KBr --à KCl + Br2
Ca + Mg2O --à CaO + 2 Mg
Li2O + Na --à no rxn
(2) Double displacement – a reaction in which the positive and negative portions of two compounds are interchanged.
MNm + M1Nm1 ---à MNm1 + M1Nm
compound + compound --à compound + compound
Examples:
PbCl2 + Li2SO4 ---à 2 LiCl + PbSO4
ZnBr2 + 2 AgNO3 --à Zn(NO3)2 + 2 AgBr
BaCl2 + KIO3 --à Ba(IO3)2 + 2 KCl
NOTE: When writing the formula for a compound the ions must have an opposite charge and the sum of the charges must equal zero.
(3) Decomposition – a reaction where a substance breaks into simpler substances when energy is applied.
A --à B + C + D
compound --à elements or compounds
There are decomposition patterns that must be followed to correctly predict the products of a decomposition reaction.
Decomposition Patterns
MNm --à M + Nm
NH4NmO --à NH3 + HNmO
NH4Nm --à NH3 + HNm
* NH4NO3 --à H2O + N2O
* NH4NO2 --à H2O + N2
MSO4 --à MO + SO2 + O2
MSO3 --à MO + SO2
MPO4 --à MO + P2O5
MPO3 --à MO + P2O3
MCO3 --à MO + CO2
MSiO3 --à MO + SiO2
MAsO4 --à MO + As2O5
MClO3 --à MCl + O2
MOH --à MO + H2O
MNO3 --à MO + NO2 + O2
* KNO3 --à KNO2 + O2
* NaNO3 --à NaNO2 + O2
* = exception
Examples:
CdCO3 --à CdO + CO2
Pb(OH)2 --à PbO + H2O
(4) Synthesis – a reaction in which two or more substance combine to form one new substance.
B + C + D --à A
element or + element or --à compound
compound compound
Synthesis patterns are the reverse of decomposition patterns.
Example:
MO + H2O --à MOH
M + Nm --à MNm
When writing a formula, do not forget that the overall charge on a compound must equal zero (be sure to consider subscripts).
Examples:
NH3 + HCl --à NH4Cl
CaO + SiO2 --à CaSiO3
2 H2 + O2 --à 2 H2O
Substitute symbols for names, predict the products, and balance.
(1) copper (II) carbonate --à
CuCO3(s) --à CuO(s) + CO2(g)
(decomposition)
(2) copper (I) + sulfur --à
2 Cu(s) + S(s) --à Cu2S(s)
(synthesis)
(3) silver nitrate + sulfuric acid --à
2 AgNO3(aq) + H2SO4(aq) --à Ag2SO4(s) + 2 HNO3
(double displacement)
Practice the following:
(1) sulfuric acid --à
(2) chromium(II) + hydrochloric acid --à
(3) ammonium nitrate --à
(4) sodium + oxygen --à
(5) calcium hydroxide + sulfuric acid --à
(6) copper(II) + silver nitrate --à
Solutions to practice:
(1) sulfuric acid --à
2 H2SO4(aq) --à 2 H2O(l) + 2 SO2(g) + O2(g)
(2) chromium(II) + hydrochloric acid --à
Cr(s) + 2 HCl(l) --à CrCl2(aq) + H2(g)
(3) ammonium nitrate --à
NH4NO3(s) --à 2 H2O(l) + N2O(g)
(4) sodium + oxygen --à
4 Na(s) + O2(g) --à 2 Na2O(s)
(5) calcium hydroxide + sulfuric acid --à
Ca(OH)2(aq) + H2SO4(aq) --à CaSO4(s) + 2 H2O(l)
(6) copper(II) + silver nitrate --à
Cu(s) + 2 AgNO3(aq) --à 2 Ag(s) + Cu(NO3)2(aq)
Mass – Mass Relationships
Problem: How much reactant is needed to react with a specific amount of another reactant? How much product can be expected from a specific mass of reactant?
We use balanced equations to solve problems involving a chemical reaction. Calculations such as these are called mass-mass problems.
Mass-mass problems involve finding the mass of one substance from the given mass of another substance.
Example:
How many grams of silver chloride can be produced from the reaction of 17.0 g of silver nitrate with excess sodium chloride?
(1) Write an equation and balance.
AgNO3(aq) + NaCl(aq) --àAgCl(s) + NaNO3(aq)
17.0 g
(2) Find the number of moles of the given substance and the required substance.
(3) Use the balanced equation to determine the ratio of the moles or required substance to moles of a given substance.
NOTE: The coefficients in a balanced equation indicate the number of moles of reactants used and products produced in a chemical reaction.
(4) Express the moles of required substance in terms of grams.
Example:
How many grams of Cu2S could be produced from 9.9 g of CuCl reacting with an excess of H2S gas?
Example:
How many grams of calcium hydroxide will be needed to react completely with 10 grams of phosphoric acid?
Mass-Mass Problems
(1) Given the following equation:
2 KClO3 --à 2 KCl + 3 O2
How many moles of O2 can be produced by letting 12.00 moles of KClO3 react?
(2) Given the equation:
2 K + Cl2 --à 2 KCl
How many grams of KCl are produced from 2.50 g of K and excess Cl2? From 1.00 g and excess K?
(3) Given the equation:
Na2O + H2O --à 2 NaOH
How many grams of NaOH are produced from 1.20 x 102 grams of Na2O? How many grams of Na2O are required to produce 1.60 x 102 grams of NaOH?
(4) Given the following equation:
Cu + 2 AgNO3 --à Cu(NO3)2 + 2 Ag
How many moles of Cu are needed to react with 3.50 moles of AgNO3? If 89.5 g of Ag were produced, how many grams of Cu reacted?