Combustion

Students will identify and balance combustion

reactions

A hydrocarbon is chemical compound that only contains carbon and hydrogen

What is a Hydrocarbon?

An alkane is a hydrocarbon that has the general formula of CXH2X + 2

C3H8 and C5H12 are examples of alkanes.

What is an Alkane?

Most alkanes are named after the number of carbon atoms.

The name

C5H12 = pentane

C8H18 = octane

Names of Alkanes

These numbers are the fuels octane rating.

The octane rating is the resistance of the fuel to autoignition

Octane Ratings

Octane Ratings are based on the combustion of these two molecules.

The products (if burned in open air) are water and carbon dioxide

Products in Combustion

When hydrocarbons burn in enclosed areas, they can also produce CO which is a deadly gas.

DANGER!

Air is mostly two types of gasses. N2 which has a mass of 28 grams/mole O2 which has a mass of 32 grams/mole

Methane (CH4) has a mass of 16grams/ mole

FYI: H2 = 2 grams/ mole is the lightest gas Propane C3H8 has a mass of 44grams/mole

is heavier than air which makes it more dangerous

Why do the bubbles float?

CH4 only has a small window of mixtures that burn. Methane only burns in mixtures between

4.4 – 15% methane to air

Acetylene burns 2.5 – 82%

See Wikipedia http://en.wikipedia.org/wiki/Flammability_limit

Why does the gas burn so slowly?

The candle supplies the energy to get the methane to start burning.

However, ones it starts, it supplies its own energy to react with the oxygen.

Energy Diagram

POTENTIAL ENERGY