Chemistry
HS/Science
Unit: 08 Lesson: 01
The Mathematics of the Combustion Reaction
All automobile and jet engines depend on the burning of fuel to transform chemical energy into the
mechanical energy needed to turn wheels and propel airplanes. The chemical process in which a
fuel reacts rapidly with oxygen and gives off heat and exhaust is called combustion and is shown
below.
Heat
Heat
Let’s review some fundamentals.
Typical fuels (examples are propane, gasoline, and jet fuel) are
hydrocarbons, molecular compounds composed of carbon and hydrogen.
Combustion
requires a source of energy (such as heat or a spark) to start the chemical reaction
Fuel
COMBUSTION
between the fuel and oxygen. If any one were missing,
there would be no combustion.
Once the combustion reaction gets started, the heat of the reaction provides the energy to keep the
reaction going. And the reaction
Oxygencan be a slow burn, such as on a propane stove, or an explosion,
such as in a gasoline automobile engine.
•
Exhaust
Draw an arrow on the diagram above to show how combustion uses the heat that it
generates to keep the reaction going.
During combustion of hydrocarbons, new chemical substances are created. When the combustion
is complete, these substances, called exhaust, are water vapor (H2O) and carbon dioxide gas
(CO2). Sometimes, the combustion is not complete and soot (solid particulate carbon) is formed.
Complete combustion of a hydrocarbon  carbon dioxide (CO2) and water (H2O)
•
Methane is CH4 and propane is C3H8. Label the drawing above with the correct formulas for
the fuels and the exhaust products.
©2012, TESCCC
05/08/13
page 1 of 2
Chemistry
HS/Science
Unit: 08 Lesson: 01
Challenge One
Methane, a colorless, odorless gas, is the main component of natural gas. (An odorant is added to
natural gas for this reason!) Methane is the main ingredient in the explosive “firedamp” of
coalmines. Although it is not toxic, breathing methane can cause suffocation by displacing oxygen
in your lungs. In the chemical industry, methane is used to produce methanol and formaldehyde,
but its principal use is as a fuel. The combustion of methane releases a large amount of heat. Using
dimensional analysis, determine how much carbon dioxide could be formed during the complete
combustion of 32.0 g methane with sufficient oxygen.
Challenge Two
Methane can also be manufactured by distilling coal. Coal contains mostly carbon, but also
methane, benzene, and naphthalene, as well as small amounts of other elements and compounds.
Suppose the combustion of methane in the presence of sufficient oxygen has produced 90.0 grams
of water. How much methane was used? Use dimensional analysis.
Challenge Three
Propane is also a colorless and odorless, clean-burning fuel like methane. It is also non-toxic and
has a foul-smelling substance, called a mercaptan, added to make leaks easily detectable. Engines
using propane produce fewer harmful exhaust emissions than gasoline engines, making it a more
environmentally friendly fuel for transportation. If 880.0 grams of propane were combined with
enough oxygen, how much water would be formed? Use dimensional analysis.
Challenge Four
Many people in rural Texas use propane stored in large tanks as their source of energy for heating,
cooking, drying clothes, powering farm equipment, and running irrigation pumps. If the propane tank
on a small barbeque grill contains 440.0 grams of propane, how much carbon dioxide will be formed
by the complete combustion of all of the propane in the tank? Use dimensional analysis.
Challenge Five
Using the information provided on combustion of different hydrocarbons, design a group challenge
using the chemical reactions for hydrocarbon combustion. Write the challenge so that another group
will be interested in the problem, understand the chemical question, and be able to provide an
answer to the challenge with the information provided. Exchange challenges, and complete the
calculations for other group challenges in your class.
©2012, TESCCC
05/08/13
page 2 of 2