Chemical ReactionsChemical Reactions

Five Types of Chemical Reactions:

1. Combustion

3. Decomposition

4. Single Displacement

5. Double Displacement

2. Synthesis

Evidence that a chemical reaction Evidence that a chemical reaction has taken place?has taken place?

Colour / Odour Change

Formation of a gas or solid

Difficult to reverse

Release/Absorption of Energy (heat)

More commonly known as burning

1. Combustion Reactions1. Combustion Reactions

Easily identified (release of heat)

HeatFuel

For combustion 3 things need to be present:

Oxygen

1. Combustion Reactions1. Combustion Reactions

Sulphur (in gasoline):

S(s) + O2(g) SO2(g) + Heat

2 H2(l) + O2(l) 2 H2O(g) + Heat

Rocket Fuel:

Common OxidesCommon OxidesResulting from Combustion ReactionsResulting from Combustion Reactions

Combustion SituationElement in

Reactant

Common

Oxide

Coal in a coal-fired electricity generator carbon CO2 (g)

Burning of rocket fuel Hydrogen H2O (g)

Commercial production of sulphuric acid Sulphur SO2 (g)

Lightning strikes and volcanoes Nitrogren NO2 (g)

2. Synthesis Reactions2. Synthesis Reactions

combination of two or more simple substances combining to form a more complex substance.

A + B AB

+

MgMg(s)(s) + O + O2(g)2(g) MgO MgO22

Synthesis of Magnesium Oxide

Other ExamplesOther Examples

C(s) + O2(g) CO2(g)

S(s) + O2(g) SO2(g)

Synthesis Reactions:

3. Decomposition Reactions3. Decomposition Reactions

Breaking down large, complex molecules or ionic compounds into smaller, simpler entities.

AB A + B

+

HH22OO2(l)2(l) O O2(g)2(g) + H + H22OO(l)(l)

Decomposition of Hydrogen PeroxideDecomposition of Hydrogen Peroxide

2 2

4. Single Displacement4. Single Displacement

reaction of an element with a compound that produces a new element and new compound.

A + BC AC + B

Single Displacement of Zinc and ChlorineSingle Displacement of Zinc and Chlorine

HClHCl(aq)(aq) + Zn + Zn(s) (s) H H2(g)2(g) + ZnCl + ZnCl2(aq)2(aq)2

Chemical Reactions in SolutionChemical Reactions in Solution

SOLUTE – is a pure substance (usually lesser in quantity) that is dissolved in another pure substance called the “SOLVENT”

AQUEOUS SOLUTION – a solution in which water is the solvent (aqua – meaning water).

SolubilitySolubilitySolutions are homogenous mixtures of solutes and

solvents.

Solubility is the measure of how much of the solute can possibly dissolve in a known amount of solvent. If a substance has high solubility in water, it has a subscript of (aq). However, if it isn’t very soluble it will start to precipitate out and will have a (s) subscript for solid.

Use a Solubility TableUse a Solubility Table

Is calcium hydroxide soluble? Is sodium flouride soluble?What about lead (II) Iodide?

5. Double Displacement5. Double Displacement

reaction of two compounds, where the positive and negative ions in their respective compounds switch places to form two new compounds. This can only happen with ionic compounds

AB + CD AD + CB

Double DisplacementDouble Displacement

A double displacement reaction only occurs if one of the following three results are seen:

a precipitate is formed a gas is produced a change of pH occurs (a neutralization reaction)

** If the products are both soluble then the reaction is NR (no reaction)

Double Displacement of Lead and PotassiumDouble Displacement of Lead and Potassium

Pb(NOPb(NO33))2(aq)2(aq) + KI + KI(aq) (aq) PbI PbI2(s)2(s) + KNO + KNO3(aq)3(aq)22

Precipitate: A solid that is formed as a result of the chemical reaction of two aqueous solutions.

More ExamplesMore Examples

FeCl3(aq) + Na2(SO4)2(aq) → ?

NR – both are soluble

HCl(aq) + LiOH(aq) → ?

pH change – neutralization reaction, products are LiCl & H2O

2HNO3(aq)+ K2CO3(aq)→ CO2(g)+H2O(l) + 2 KNO3(aq)

gas produced – therefore double displacement

Percentage CompositionPercentage Composition

Composition of Common

Alloys

Alloy % Composition Property

Brass Cu (70%)

Zn (30%)

Harder and more resistant to corrosion than copper

Stainless Steel

Fe (80%)

Cr (18%)

Ni (1%)

Si (1%)

More resistant to corrosion then iron

18K gold Au (75%)

Ag (13%)

Cu (12%)

Harder and less malleable than 24K gold

Percent CompositionPercent Composition Percentages are calculated by weight

How much gold (in grams) is there in 10g sample of 18K yellow gold where the % composition is 75% Au?

Answer: mass of Au = (75% / 100) x 10g

= 7.5 g

Therefore there is 7.5 g of pure gold in a 10g sample of 18K yellow gold.