There are 4 different definitions to describe the mole depending on how it is used. Interestingly they all interrelate, even though they are different.

Everyone knows that a dozen represents 12 items such as eggs or donuts. Just like a dozen, the mole represents a numerical value. When you "know the mole" you will remember that a mole will always equal 6.02 X 10²³ items. With such a huge number, the items that we are counting are very small, such as atoms or molecules (a group of bonded atoms that form a larger structure).

People who "know the mole" remember that 1 mole of any gas will always have a volume of 22.4 Liters when the gas is at standard temperature & pressure (the gas is at 0^oC and sea level air pressure).

Remember: Even if the 1 mole of gas is moving around in the form of small atoms or huge gas molecules, both volumes will be 22.4 L since there are 6.02 X 10²³ atoms or molecules of gas.

For information about experiments that help to understand the size of a mole of gas (22.4Liters) Click Here

When you "know the mole" you will realize that the number of moles of one substance can be compared to another. These mole comparisons can be within a formula or between two formulas within a balanced equation. This is accomplished by using the formula's subscripts (small numbers in the lower right corner) &/or coefficient (large number in front of the formula).

Hint: The total number of moles for each element can be calculated by multiplying the coefficient by the subscript.

Examples:

A) CO₂ : There is 1 mole of C & 2 moles of oxygen to make 1 mole of CO₂

B) 4Fe₂O₃ : There are 8 moles of Fe and 12 moles of oxygen in 4 moles of Fe₂O₃

C) The balanced equation for burning ethane is: 2C₂H₆+ 7O₂ --->6H₂O + 4CO₂

To do examples 1 - 3 below, use the balanced equation above.

1) When comparing oxygen to water, there are 7 moles of O₂ needed to make 6 moles of H₂O.

2) When comparing carbon dioxide to ethane, to make 4 moles of CO₂ you need 2 moles C₂H₆.

3) When comparing ethane to oxygen, to have the ethane burn perfectly it will require a ratio of 2 moles of C₂H₆ to 7 moles of O₂.

When the world "knows the mole" we will all understand that the mass in grams of 1 mole of any substance is the same number as its atomic mass (the decimal number in the Periodic Table).

Examples:

1 atom of carbon = 12.01 atomic mass units

1 mole of carbon = 12.01 grams (Because there are 6.02 X 10²³ atoms of carbon).

1 molecule of H₂O = (H-1.01 + H-1.01 + Oxy-16.00) = 18.02 atomic mass units

1 mole of H2O = 18.02 grams (Because there are 6.02 X 10²³ molecules of water).

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