Stoichiometry

Review: Dimensional Analysis Goal: To make the units cancel out Strategy: Start out with the quantity given that you are trying to convert Using a conversion factor, multiply so that the units cancel out. You can’t cancel out units if you don’t write them out!!

Chapter Goals: The Road Map Volume (L) Mass (g) Molecules, atoms, formula units In this chapter there are three basic types of problems…. You will be asked to reproduce this “map” on the test. The MOLE

First Route: Moles to molecules Molecules, atoms, formula units The MOLE

Moles to Molecules When we convert moles to: molecules, atoms, formula units, etc, we use the following conversion factors:

Example How many molecules are in 2.00 moles of sucrose?

Examples How many moles are in 2.33 x molecules of water? How many atoms are in 2.95 moles of Au?

Road 2: Moles to Mass Mass (g) Molecules, atoms, formula units The MOLE

Converting Moles to Grams (the most common calculation!) We use molar mass as a conversion factor:

Example Calculate the number of moles in 75.0 g dinitrogen trioxide.

Examples Calculate the mass, in g, of moles of sodium chloride. Calculate the number of moles in 75.0 g of nitrogen gas.

Chapter Goals: The Road Map The MOLE Mass (g) Molecules, atoms, formula units Volume (L)

Converting Moles to Volume One mole of ANY gas will expand to have a volume of 22.4 L at STP. STP = Standard Temperature and Pressure Standard Temp: 0 degrees C Standard Pressure: 1 atm = kPa 22.4 L is called MOLAR VOLUME (the volume of one mole of a gas)

Molar Volume The conversion factors (always):

Example How many moles of N 2 are in 120 L of gas?

More examples What is the volume of 2.54 moles of methane gas? How many moles are in 6 L of H 2 gas?

Warm-Up 2/22/16 How many grams are in 12 L of O 2 gas? How many moles are in 31 grams of calcium phosphate? How many atoms are in 5 moles of argon?

Summary Follow the road map! Moles  L or L  moles: molar volume Moles  g or g  moles: molar mass

If none of the above… Moles  particles, atoms, molecules, Formula Units: Avogadro’s number

How many L of oxygen gas (at STP) are in 6.5 x molecules of oxygen gas?

Review What did all the equations with the Mole Road Map have in common? All had only one compound or sample What if I have a chemical reaction instead of a single compound?

Review Why did we balance chemical equations? Law of Conservation of Mass ___N 2 (g) + ____H 2 (g)  ____NH 3 (g) The coefficients are in moles!

Using the Balanced Chemical Equations Balanced chemical equations give you the mole ratio N 2 (g) + 3H 2 (g)  2NH 3 (g)

The mole ratio is your conversion factor between different compounds or elements within a chemical reaction! 1 mol N 2 = 3 mol H 2 1 mol N 2 = 2 mol NH 3 3 mol H 2 = 2 mol NH 3

Example How many moles of ammonia are produced when 0.60 moles of nitrogen reacts with hydrogen? N 2 (g) + 3H 2 (g)  2NH 3 (g)

Example Calculate the number of grams of NH 3 produced by the reaction of 5.40 grams of hydrogen with an excess of nitrogen. The balanced equation is: N 2 (g) + 3H 2 (g)  2NH 3 (g)

The End