1. Unit 3: Types of Chemical Reactions
SCH3U/4C
Ms. Richardson

2. Chemical Reactions
A reaction occurs when one or more substance changes in chemical composition to form new substance(s).
We can predict the type of reaction that occurs by looking at the reactants and products.

3. Synthesis Reactions Two or more reactants combine to form one product.
General formula:
A + B  C
A B  C

4. Synthesis Reactions Synthesis reactions can occur in different ways:
Two or more reactants combine to form a binary compound
S(g) + O2(g)  SO2(g)
An element and a compound combine to form a new compound
2 SO2(g) + O2(g)  2 SO3(g)
Two compounds combine to form a new compound
SO3(g) + H2O(l)  H2SO4(aq)

5. Decomposition Reactions
One compound breaks down into two or more products.
General formula:
C  A + B

6. Decomposition Reactions
Decomposition reactions can occur in different ways:
A binary compound decomposes into its elements
2 H2O(l)  2 H2(g) + O2(g)
A metal nitrate decomposes into oxygen and a metal nitrite
2 KNO3(s)  2 KNO2(s) + O2(g)

7. Decomposition Reactions
A metal carbonate decomposes into a metal oxide and carbon dioxide
CaCO3 (l)  CaO(s) + CO2(g)
A metal hydroxide decomposes into a metal oxide and water
Ca(OH)2(s)  CaO (s) + H2O (g)

8. Single Displacement Reactions
One element takes the place of another
General formula:
AX + B  BX + A

9. Single Displacement Reactions
There are three main types of examples:
A metal displaces another metal in an ionic compound
Cu(s) + 2 AgNO3 (aq)  Cu(NO3)2(aq) + Ag(s)
A non-metal displaces another non-metal in an ionic compound
Cl2(g) + 2 NaBr (aq)  Br2(l) + 2 NaCl(aq)

10. Single Displacement Reactions
A metal displaces hydrogen from an acid or water
Mg(s) + 2 HCl(aq)  H2(g) + MgCl2(aq)
2 Na(s) + H2O(l)  H2(g) NaOH (aq)

11. Activity Series
Single displacement reactions only occur when the displaced element is less reactive than the one replacing it.
We can predict if a reaction will occur by comparing the involved elements on the activity series.

12. Activity Series of Metals

13. Example Fe(s) + CuSO4(aq)  FeSO4(aq) + Cu(s)
iron + copper (II) sulfate  iron (II) sulfate + copper
This reaction occurs because iron donates its electrons more readily than copper (iron is more reactive).
Fe(s) + AlCl3(aq)  No Reaction
Iron is less reactive than aluminum.

14. Activity Series of Nonmetals

15. Example
Cl2(g) + 2NaBr(aq)  2NaCl(aq) + Br2(g) Chlorine is more reactive than bromine, so this reaction occurs. Cl2(g) + 2NaFr(aq)  no reaction Chlorine is less reactive than fluorine, so no reaction occurs. We will show that no reaction occurs by simply writing “NR” on the products side of an equation.

16. Double Displacement Reactions
Cations exchange places in aqueous solutions.
General formula:
AX + BY  AY + BX

17. Double Displacement Reactions
A reaction may form a solid (precipitate)
Cu(NO3)2(aq) + AgCl(aq)  CuCl2(s) + AgNO3(aq)
We can predict if a precipitate will form by referring to a set of solubility guidelines that have been established based on experimental results

18. Anion
+ Cation
 Solubility of Compound 1
Most
Alkali metal ions (Li+, K+, Rb+, Cs+, Fr+)
Soluble
Hydrogen ion (H+)
Ammonium ion (NH4+) 2
Nitrate (NO3-)
Acetate (CH3COO-)
Ag+
Low solubility
Most others 3
Chloride (Cl-)
Bromide (Br-), Iodide (I-)
Ag+, Pb+, Hg2+, Cu+, Tl+
All others 4.
Flouride (F-)
Mg2+, Ca2+, Ba2+, Pb2+
Low solubiity 5.
Sulfate (SO42-)
Ca2+, Sr2+,Ba2+, Pb2+ 6.
Sulfide (S2-)
Alkali ions and H+, NH4+, Be2+, Mg2+, Ca2+, Sr2+, Ba2+ 7
Hydroxide (OH-)
Alkali ions and H+, NH4+, Sr2+, Ba2+, Tl+ 8
Phosphate (PO43-)
Alkali ions and H+, NH4+

19. Example
Magnesium chloride and lead (II) acetate form a precipitate. Predict the products and write a balanced equation identifying the precipitate.

20. Solve Identify the ions that make up each reactant.
Magnesium chloride: Mg2+, Cl-
Lead acetate: Pb2+, CH3COO-
Switch the pairs of ions to determine the products, and write the equation.
MgCl2(aq) + Pb(CH3COO)2(aq)  Mg(CH3COO)2 + PbCl2

21. Use the solubility guidelines to determine the precipitate.
Acetate is soluble with magnesium
Lead (II) ions have low solubility with chloride ions.
MgCl2(aq) + Pb(CH3COO)2(aq)  Mg(CH3COO)2(aq) + PbCl2(s)

22. Double Displacement Reactions
A reaction may form a gas
NaOH(aq) + NH4Cl (aq) HOH(l) + NaCl(aq) + NH3(g)
A reaction may form water
H2SO4(aq) + 2 NaOH(aq)  2 HOH(l) + Na2SO4(aq)

23. Summary of Double Displacement Reactions
If one reactant…
+ the other reactant…
 then the products include
is an aqueous salt
a precipitate
is an acid
has carbonate ions
water and carbon dioxide
has ammonium ions
has hydroxide ions
water and ammonia
water

24. Specialized Chemical Reactions
Neutralization Reactions:
Specific type of double displacement reaction involving acids and bases:
General Formula:
acid + base  salt + water
Example:
HCl + NaOH  NaCl + HOH

25. Specialized Chemical Reactions
Combustion Reactions:
Oxygen combines with another substance to produce energy (heat and light) and one or more oxides

26. Combustion Reactions Hydrocarbon Combustion: Complete Combustion:
A hydrocarbon reacts with an abundant amount of oxygen gas to produce water and carbon dioxide
Incomplete Combustion:
A hydrogen combustion reaction with a poor supply of oxygen which produces any combination of CO2, H2O, CO and C (soot)

27. Specialized Chemical Reactions
Oxides and Water:
Metal oxides combine with water to produce hydrogen gas and metallic hydroxides.
The resulting metallic hydroxide solution is a basic solution.
BaO(s) + 2 H2O (l)  H2 (g) + Ba(OH)2 (aq)
Na2O(s) + 2 H2O (l)  H2 (g) + 2 NaOH (aq)

28. Specialized Chemical Reactions
Non-metallic oxides combine with water to produce acidic solutions (oxyacids).
CO2 (g) + H2O (l)  H2CO3 (aq)
P4O10 (s) + 6 H2O (l)  4 H3PO4 (aq)