Types of Chemical Reactions let’s classify...

Why Classify Chemical Reactions? “I wonder what will happen if I light a match in a room full of gasoline vapour?” What type of reaction do you think will occur? Combustion—exothermic and rapid! How do you know this?

Five Types of Chemical Reactions 1.Synthesis 2.Decomposition 3.Combustion 4.Single Displacement 5.Double Displacement let’s look more closely at each type...

Synthesis Reactions Occur when two or more elements or compounds combine to form a new substance. These reactions come in the general form of: A + B  AB eg. 8 Fe + S 8  8 FeS

Predict the products... Na(s) + Cl 2 (g)  NaCl(s) Al(s) + Br 2 (l)  AlBr 3 (s) Fe(s) + Cl 2 (g)  FeCl 3 (s)

Mg(s) + O 2 (g)  MgO(s) Sb(s) + Cl 2 (g)  SbCl 3 (s)

P 4 (s) + O 2 (g)  P 4 O 10 (s) P 4 O 10 (s) + HOH(l)  H 3 PO 4 (aq) CaO + HOH(l)  Ca(OH) 2 (aq)

Reactions of Oxides with Water a) Metal oxide + HOH  basic solution eg. Na 2 O(s) + HOH(l)  NaOH(aq) b) Non-metallic oxide + HOH  acidic solution eg. SO 3 (g) + HOH(l)  H 2 SO 4 (aq)

Write the product(s) of each of the following synthesis reactions Zn(s) + S 8 (s)  ZnS(s) Zn(s) + O 2 (g)  ZnO(s) S 8 (s) + O 2 (g)  SO 2 (g)

Synthesis reactions and Acid Precipitation CO 2 (g) + H 2 O(l)  H 2 CO 3 (aq) S 8 (s) + O 2 (g)  (unbalanced) SO 2 (g) SO 2 (g) + O 2  (unbalanced) SO 3 (g) SO 3 (g) + H 2 O(l)  (unbalanced) H 2 SO 4 (aq)

Decomposition Reactions A compound decomposes—or breaks down into its elements or into other compounds. C  A + B A decomp. reaction is the opposite of a synthesis reaction.

Types of Decomposition Rxns binary cmpd  its elements metal nitrate  metal nitrite + O 2 metal carbonate  metal oxide + CO 2 metal hydroxide  metal oxide + H 2 O

Examples NaCl(s)  Na(s) + Cl 2 (g) KNO 3 (s)  KNO 2 (s) + O 2 Na 2 CO 3  Na 2 O + CO 2 NaOH  Na 2 O + H 2 O

Examples of decomposition reactions 2 HOH(l)  2 H 2 (g) + O 2 (g) NH 4 NO 3 (s)  N 2 O(g) + 2 HOH(g) H 2 O 2 (aq) (with MnO 2 (s) catalyst)  HOH(l) + O 2 (g)

What’s a catalyst? A catalyst increases the rate of a chemical reaction... but is not used up in the reaction. A catalyst is present at the beginning and at the end of a chemical reaction. eg. catalytic converter in an automobile’s exhaust system

More examples of decomp rxns (with video clips) KClO 3 (s) + heat  KCl(s) + O 2 (g) (NH 4 ) 2 Cr 2 O 7 (s) + heat  Cr 2 O 3 (s) + N 2 (g) + HOH(g)

Are the products of a decomposition reaction stable or unstable compounds? What product(s) have you noticed so far? N 2, HOH, KCl, etc These are all stable compounds.

Q: What is Beethoven doing in his grave? A: Decomposing

Combustion Reactions Used for cooking, heat, transportation and more. Complete combustion of a C & H (& O) containing fuel in the presence of sufficient O 2 yields CO 2 and HOH Incomplete combustion yields C(s) + CO(g) + CO 2 (g) + H 2 O(g)

examples of combustion of C&H(&O) - containing fuels CH 3 CH 2 OH(l) + O 2 (g)  (sufficient O 2 ) CO 2 (g) + HOH(g) C 8 H 18 (l) + O 2 (g)  incomplete combustion C(s) + CO(g) + CO 2 (g) + HOH(g) (Incomplete combustion—not enough O 2 present) Is it possible to balance this equation?

Here’s an example of just how combustible methane is:

Here’s what happened when we put a balloon full of H 2 and O 2 on top of a sheet of Al foil in a microwave oven. rxn is: 2 H 2 (g) + O 2 (g)  2 H 2 O(g) + energy

Can also have combustion of elements other than carbon eg. Mg(s) + O 2 (g)  MgO(s) H 2 (g) + O 2 (g)  HOH(g) How else could we classify these reactions? synthesis

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