3.4 A World Of

Reactions

YEAR 10 SCIENCE 2012 – CHEMISTRY UNIT

Types of reactions • There are five main types of chemical reactions we

will talk about:1) Combination reactions2) Decomposition reactions3) Single displacement reactions4) Double displacement reactions5) Combustion reactions

• You need to be able to identify the type of reaction and predict the product(s)

Types of reactions • Some steps for doing reactions

1) Identify the type of reaction2) Predict the product(s) using the type of reaction

as a model3) Write a worded equation for the reaction4) Balance it –the formulae & the equation

• Don’t forget to check the states of matter:• (s) = solid; (l) = liquid; (g) = gas; • (aq) = aqeous = soluble salt dissolved in water

COMBINATION reactions • Combination reactions occur when two substances

(generally elements) combine and form a compound. • Sometimes these are called synthesis or addition

reactions.

reactant + reactant 1 productA + B AB

• Example: 2H2 + O2 2H2O • Example: C + O2 CO2

COMBINATION reactions

COMBINATION reactions • Predict the products. Write and balance the following

synthesis reaction equations.

• Sodium metal reacts with chlorine gas

• Solid Magnesium reacts with fluorine gas

• Aluminum metal reacts with fluorine gas

DECOMPOSITION reactions • Decomposition reactions occur when a compound

breaks up into the elements or in a few to simpler compounds

1 reactant product + productAB A + B

• Example: 2 H2O 2H2 + O2

• Example: 2 HgO 2Hg + O2

DECOMPOSITION reactions

DECOMPOSITION reactions • Predict the products. Then, write and balance the

following decomposition reaction equations.

• Solid Lead (IV) oxide decomposes

• Aluminum nitride decomposes

SINGLE DISPLACEMENT reactions

• Single Displacement Reactions occur when one element replaces another in a compound.

• Two displacements are possible:• a metal can replace a metal (+ ions) • a non-metal can replace a non-metal (- ions).

SINGLE DISPLACEMENT reactions

element + compound element + compoundA + BC AC + B (if A is a metal)

A + BC BA + C (if A is a non-metal)

SINGLE DISPLACEMENT reactions

• Write and balance the following single replacement reaction equation: • Zinc metal reacts with aqueous hydrochloric acid

• Sodium chloride solid reacts with fluorine gas

• Aluminum metal reacts with aqueous copper (II) nitrate

SINGLE DISPLACEMENT reactions

Double DISPLACEMENT reactions

• Double Replacement Reactions occur when a metal replaces a metal in a compound and a non-metal replaces a non-metal in a compound

Compound + compound compound+ compound

AB + CD AD + CB

DOUBLE DISPLACEMENT reactions

• Example:• Solid sodium chloride is dissolved into silver nitrate

solution:AgNO3 (aq) + NaCl (s) AgCl (s) + NaNO3 (aq)

• Another example:• Two solutions of potassium sulfate and barium

nitrate are mixed together: K2SO4 (aq) + Ba(NO3)2 (aq) 2 KNO3 (aq) + BaSO4 (s)

• Predict the products. Balance the equations:

1. Hydrochloric acid + silver nitrate2. Calcium chloride + sodium phosphate3. Lead (II) nitrate + barium chloride4. Iron (III) cholride + sodium hydroxide5. Sulfuric acid + sodium hydroxide6. Potassium hydroxide + copper sulfate

DOUBLE DISPLACEMENT reactions

Combustion reactions • Combustion reactions occur when a hydrocarbon

reacts with oxygen gas.• This is also called burning!!! • In order to burn something you need the 3 things in

the “fire triangle”:1) A Fuel (hydrocarbon)2) Oxygen to burn it with3) Something to ignite the reaction (spark)

Combustion reactions • In general:

CxHy + O2 CO2 + H2O

• Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide)

• Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)

Combustion reactions • Example• pentane (C5H12) + O2 CO2 + H2O

• Write the products of the following combustion reaction:

• Combustion of decane

CORROSION reactions • Type of combination reaction.• Oxygen combines with a metal to form an ionic

compound.

metal + O2 metal oxide

Precipitation reactions• Type of double displacement reaction.• Two solutions of soluble salts are mixed, resulting in

an insoluble solid (precipitate) forming.

Soluble salt A(aq) + Soluble salt B(aq) precipitate(S) + Soluble salt C(aq)

Precipitation reactions• Solubility rules are needed to work out whether a

precipitate will form.Ions Form a soluble compound when

joined with these ionsForm an insoluble compound when

joined with these ions

Sodium, Ammonium, Potassium, Lithium, Nitrate

All None

Chloride, Bromide, Iodide

All (with exceptions)Silver

MercuryLead

Sulphate All (with exceptions)Barium

LeadCalcium

Carbonate, Phosphate and Hydroxide

SodiumAmmoniumPotassium

LithiumAll (with exceptions)

Neutralisation reaction• Type of double displacement reaction.• An acid and a base react with each other. • Generally, the product of this reaction is a salt and

water.

acid + base salt + water

Acid + metal reaction• Type of single displacement reaction.• An acid and a metal react with each other. • Generally, the product of this reaction is a salt and

hydrogen gas.

acid + metal salt + H2

Acid + metal carbonate reaction• An acid and a metal carbonate react with each other. • Generally, the product of this reaction is a salt, water

and carbon dioxide gas.

acid + metal carbonate salt + H2O + CO2

PRACTICEIdentify the type of reaction and try to write a correctly balanced chemical equation for each of the following reactions:Copper + silver nitrate silver + copper nitrateLead nitrate + potassium iodide lead iodide +

potassium nitrateMethane gas + oxygen carbon dioxide + waterZinc carbonate zinc oxide + carbon dioxideMagnesium + oxygen magnesium oxideCorrosion of zinc