5 Steps to a 5 AP Chemistry 2019

Reactions and Periodicity ‹ 77

The Groups IA and IIA elements on the activity table will displace hydrogen from

water, but not the other metals shown. All the metals above hydrogen will react with acidic

solutions to produce hydrogen gas:

+→+

+→+++

Co(s)2HCl(aq)CoCl(aq)H(g)

Co(s)2H(aq)Co(aq)H(g)

22

2

2

Halogen reactivity decreases as one goes from top to bottom in the periodic table,

because of the decreasing electronegativity. Therefore, a separate activity series for the

halogens can be developed:

F

Cl

Br

I

2

2

2

2

The above series indicates that if chlorine gas were dissolved in a KI(aq) solution, the

elemental chlorine would displace the iodide ion:

+→ +

+→−−+

Cl (aq) 2KI(aq)2KCl(aq)I(s)

Cl (aq) 2I(aq) 2Cl(aq)I(s)

22

22

Combustion Reactions

Combustion reactions are redox reactions in which the chemical species rapidly com-

bines with oxygen and usually emits heat and light. Reactions of this type are extremely

important in our society as the sources of heat energy. Complete combustion of carbon

yields carbon dioxide, and complete combustion of hydrogen yields water. The complete

combustion of hydrocarbons, organic compounds containing only carbon and hydrogen,

yields carbon dioxide and water:

2C 26 H(g)+→7O 22 (g)4CO(g)6+ HO 2 (g)

If the compound also contains oxygen, such as in alcohols, ethers, etc., the products are

still carbon dioxide and water:

2CHO 32 H(l)+→3O(g)2CO 22 (g)4+ HO(g)

If the compound contains sulfur, the complete combustion produces sulfur dioxide, SO 2 :

2C 26 HS(g)9+→O( 22 g) 4CO(g)++6H 22 O(g) 2SO(g)

If nitrogen is present, it will normally form the very stable nitrogen gas, N 2.

In all of these reactions, the driving force is the highly reactive oxygen forming a very

stable compound(s). This is shown by the exothermic nature of the reaction.

In balancing any of these combustion reactions, it is helpful to balance the oxygen last.

Coordination Compounds

When a salt is dissolved in water, the metal ions, especially transition metal ions, form

a complex ion with water molecules and/or other species. A complex ion is composed of a metal

ion bonded to two or more molecules or ions called ligands. These are Lewis acid–base

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