Propane in 3-D

Now the eggheads will tell you that propane looks like this:

Lewis Structure

A fellow named Lewis will tell you that it looks like this:

Propane at its Best

But I think propane looks a little more like this:

Now, doesn’t that look the best of all?

Grilled to perfection using propane: a fantastic gas.

PROPANE is an exciting fuel molecule belonging to the group of hydrocarbons known as alkanes.

Its formula is C3H8. Its molar mass is 44.09 g/mol.

Propane is Not Flat

Lewis’ model might make you think that propane is flat… but this is not true…propane utilizes all three of its dimensions to their fullest potential in grilling the perfect steak.

Each of the carbons in propane has a delicious tetrahedral geometry, leading to the indicated red bond angles of approximately 109.5 degrees.

The C-C bond length is a delectable 0 .154 nm and the C-H bond length is a savory 0.109 nm.

Propane is Nonpolar

Since carbon and hydrogen have similar electronegativities (2.5 for C and 2.2 for H) the C-H bonds in propane are almost absolutely covalent (EN difference = 0.3).

One would call them “nonpolar”.

Of course, the C-C bonds are absolutely covalent (and also, of course, nonpolar).

In fact, propane is a totally nonpolar molecule – it has no dipoles.

You might think this makes propane on the boring side… but this assessment is totally negated with the addition of oxygen and a flame (see delicious steak in another post). But more on that later. Suffice it to say for now that no polarity surprises will explode in your face if you go with propane!

Without dipoles, the only intermolecular forces possible in propane are dispersion forces, which come from the creation of temporary (induced) dipoles in these molecules. These weak intermolecular forces make propane molecules not all that attracted to each other, leading to a low boiling point of -42.1 degrees C.

Propane’s freezing point is much lower, at -187.7 degrees C. Now that’s COLD.

What's in the Tank?

Now these same eggheads mentioned earlier will tell you that in a tank of propane the gas is liquefied. But how can this be when propane is a gas at room temperature?

Well, the answer lies in the propane tank itself, where propane is held at a moderately high pressure of between about 5 and 10 atm. The picture at right shows the propane liquid as black and the propane gas above it as yellow. The yellow bubbles are also propane gas.

As a liquid, propane is much easier to store, with a liquid density (at the boiling point) of 582 kg per cubic meter as opposed to a gas density (at the boiling point) of 2.423 kg per cubic meter. This means the same mass of liquid would take up 240 times less space as the gas – meaning you get a lot more bang for each cubic meter!

Propane Combustion

The most succulent property of propane is its ability to combust in air (oxygen).

This is a picture of propane combustion.

Propane reacts with oxygen in the reaction given here:

C3H8 (g) + 5 O2 (g) --> 3 CO2 (g) + 4 H2O (l)

Each mole of propane releases 2220 kJ of heat!

But the end result is absolutely delectable, as the heat and flames produce meats and vegetables grilled just the way you like them!

Most folks would agree that this truly makes PROPANE a FANTASTIC GAS.