Basic chemistry help for students and teachers

 

Interactive Chemistry Worksheets for Students

 

Periodic table

Naming compounds

Basic formula

Simple compounds

Ionic compounds 1

Ionic compounds 2

Chemical suffixes

Old chemical names

Hydrocarbons - Alkanes

Alkanes, alkenes & alkynes

Alkanols to alkanoic acids

 

Common compounds

Common formula quiz

Acids, bases and salts

Covalent compounds

Printable worksheets
 

 

 

What is a hydrocarbon?

Hydrocarbons are compounds that contain the elements hydrogen and carbon. They are obtained by the fractional distillation of crude oil.

Hydrocarbons can be divided into three main groups, alkanes, alkenes and alkynes.

Examples of hydrocarbons are propane, C3H8 and octane, C8H18

Carbon atoms Alkane, CnH2n+2 Alkene, CnH2n Alkyne, CnH2n-2
1 methane, CH4 NA NA
2 ethane, C2H6 ethene, C2H4 ethyne, C2H2
3 propane, C3H8 propene, C3H6 propyne, C3H4
4 butane, C4H10 butene, C4H8 butyne, C4H6
5 pentane, C5H12 pentene, C5H10 pentyne, C5H8
6 hexane, C6H14 hexene, C6H12 hexyne, C6H10
7 heptane, C7H16 heptene, C7H14 heptyne, C7H12
8 octane, C8H18 octene, C8H16 octyne, C8H14
9 nonane, C9H20 nonene, C9H18 nonyne, C9H16
10 decane, C10H22 decene, C10H20 decyne, C10H18

 

What is combustion?

Combustion is a self-sustaining chemical reaction in which heat is produced by the burning of a fuel with oxygen.

Note: In Senior Chemistry fuels can be burnt in other substances like chlorine. These substances act in the same way as oxygen and are called oxidizing agents.

 

How to balance combustion equations

A helpful aid in balancing combustion equations is to balance each element in alphabetical order, C H O

Balance the carbon atoms first, hydrogen atoms second and oxygen atoms last, C H O

 

Examples

1. Pentane + oxygen carbon dioxide + water

C5H12 + O2 CO2 + H2O

Solution

Balance C first C5H12 + O2 5CO2 + H2O 5 C atoms are needed
Balance H second C5H12 + O2 5CO2 + 6H2O 12 H atoms are needed
Balance O third C5H12 + 3O2 5CO2 + 6H2O 6 O atoms are needed

The balanced equation for the complete combustion of pentane is

C5H12 + 3O2 5CO2 + 6H2O

 

2. Butane + oxygen carbon dioxide + water

C4H10 + O2 CO2 + H2O

Solution

Balance C first C4H10 + O2 4CO2 + H2O 4 C atoms are needed
Balance H second C4H10 + O2 4CO2 + 5H2O 10 H atoms are needed
Balance O third C4H10  + 5.5O2 4CO2 + 6H2O 11 O atoms are needed

The balanced equation can be left as a fraction as chemists deal with quantities called moles.

C4H10  + 5.5O2 4CO2 + 6H2O

The 5.5 O2 is not 5½ molecules of O2. It represents 5.5 moles of oxygen.

If you don't like working in halves then double each number in front  the formula

2C4H10 + 11O2 8CO2 + 12H2O

 

3. Ethanol + oxygen carbon dioxide + water

C2H5OH + O2 CO2 + H2O

Solution

Balance C first C2H5OH + O2 2CO2 + H2O 5 C atoms are needed
Balance H second C2H5OH + O2 2CO2 + 3H2O 6 H atoms are needed
Balance O third C2H5OH + 3O2 2CO2 + 3H2O 7 O atoms are needed

The balanced equation for the combustion of ethanol is

C2H5OH + 3O2 2CO2 + 3H2O

 

What is complete combustion?

Complete combustion is the burning of hydrocarbons in sufficient oxygen to produce carbon dioxide and water as products.

A common example of complete combustions is the blue flame of a Bunsen burner. The air hole is open.

Complete Combustion Equation

Hydrocarbon + Oxygen Carbon dioxide + water

Example

Propane + oxygen carbon dioxide + water

C3H8 + 5O2 3CO2 + 4H2O

 

What is incomplete combustion?

Incomplete combustion is the burning of a hydrocarbon in insufficient oxygen producing carbon (soot), carbon monoxide and water as products.

A common example of the incomplete combustion of hydrocarbons is the yellow flame of a Bunsen burner. The air hole is closed.

a) Incomplete Combustion Equation - Multiple carbon products

Hydrocarbon + Oxygen Carbon + Carbon monoxide + water

When writing equations with incomplete combustion it is advisable to include only one carbon product otherwise there will be multiple solutions to the equation.

 

Multiple carbon products produce balanced equations with multiple solutions

 

Example

The incomplete combustion of propane, C3H8 produces two possible balanced equations.

C3H8 + 3 O2 2CO + C + 4H2O

C3H8 + 2.5 O2 CO + 2C + 4H2O

 

b) Incomplete Combustion Equation - Single carbon product

Hydrocarbon + Oxygen Carbon monoxide + water

and

Hydrocarbon + Oxygen Carbon + water

 

When there is only one carbon product there is only one solution to each equation.

 

Example

If the product is only carbon monoxide CO, there is only one solution to the balanced equation.

C3H8 + 4 O2 3 CO + 5H2O

and

If the product is only soot C, there is only one solution to the balanced equation.

C3H8 + 2 O2 3C + 4H2O

 

Balancing Equations Worksheet with answers