Stoichiometry for online

Stoichiometry

Stoichiometry is the study of quantitative

relationships in chemical reactions.

The basic idea used in solving stoichiometric problems is the mole

concept.

A short review

Molecular weight is the sum of the atomic weights

of all the atoms in a molecule.

A molecule is the smallest unit of a covalent

compound.

What is a mole?

A mole (mol) is a SI base unit used to measure the amount of material in a

chemical sample.

1 mole of H2O contains 6.022 x 1023 H2O molecules

(Avogadro’s number)

A coefficient in a balanced chemical equation indicates the number of moles of a chemical

compound involved in a chemical reaction.

2H2 + O2 2H2O

The coefficients give you the mole ration of the compounds involved

in the reaction.

2H2 + O2 2H2O

The mole ratio of hydrogen to oxygen is 2:1 (for every one

oxygen put into the reaction, 2 moles of hydrogen are also

needed to put into the reaction)

The unit of moles provides a “bridge” to mathematically convert

between several different aspects of

chemical compounds.

Moles link an abstract chemical equation to a

concrete unit of measurement (grams,

Liters, number of molecules)

For example:

1 mole = 6.02 x 1023 molecules

1 mole = molecular mass of a substance

1 mole = 22.4 L of a substance at STP (standard temperature

and pressure)

For example:

1 mol Cl = 6.02 x 1023 molecules Cl 1 mol H2O = 6.02 x 1023 molecules

H2O

1 mol Cl = 35.45g Cl1 mol H2O = 18.01g H2O

1 mol Cl = 22.4L Cl @ STP 1 mol H2O = 22.4L H2O @ ATP

There are several types of calculations that can be used in Stoichiometry.

Mole – mole calculations

Involves 1 conversion factor

The object of this type of problem is to calculate the

moles of one substance when given the number of moles of

different substance.

Example: Magnesium hydroxide reacts with carbonic acid. How

many moles of water will be produced from

3.5 moles of magnesium hydroxide?

You are given the moles of one substance and asked to find the

moles of another substance.

Example: How many moles of ammonia can be produced

from 8.00 moles of hydrogen reacting with nitrogen?

Example: K2Cr2O7 + 6KI + 7H2SO4 Cr2 (SO4)3 + 4K2SO4 + 3I2 + 7H2O

Calculate the number of moles of potassium dichromate that will react with 2.0 moles of potassium iodide.

Calculate the number of moles of iodine that will be produced from 2.0

moles of potassium iodide.

Mole – mass calculations

Involves 2 conversion factors

The object of this type of problem is to calculate the

moles of one substance when given the mass of

different substance.

Or vise versa

Example: What mass of hydrogen can be

produced by reacting 6.0 moles of aluminum with

hydrochloric acid?

You are given the moles of one substance and asked to find the mass

of another substance.

Example: How much carbon dioxide is produced by the complete combustion of 0.0492 mol of propane,

C3H8?

Example: How many moles of water will be produced from 14.6 g propane in the

combustion of propane?

Mass – Mass calculations

Involves 3 conversion factors

The object of this type of problem is to calculate the

mass of one substance when given the mass of

different substance.

Example: How much carbon dioxide is produced by the complete

combustion of 100.0 g of propane, C3H8?

You are given the moles of one substance and asked to find the mass

of another substance.

Example: Magnesium chloride reacts with sulfuric

acid. How much sulfuric acid is needed to produce

26.3 g of magnesium sulfate?

Calculations involving Liters and number of

molecules

Example: How many moles of ammonia can be produced

from 1.03 Liters of hydrogen reacting with nitrogen at STP?

Example: How many carbon dioxide molecules are

produced by the complete combustion of 32.00 grams of

propane, C3H8?