Stoichiometry It’s NOT as scary as it sounds!! In fact, you have already learned 90% of it!!

What is Stoichiometry? It is the calculation of masses (grams and/or moles) of reactants and products in chemical reactions. In other words, the mathematics of chemical reactions.

What is Stoichiometry? It is the way you can figure out how much of a product to expect from given amounts of reactants or It is the way you can figure out how much of a reactant is needed to produce a desired amount of a product.

Moles Review 1) Define “mole”. 2) How many moles are present in 34 grams of Cu(OH) 2 ? 3) How many moles are present in 2.45 x molecules of CH 4 ? 4)How many grams are there in 3.4 x molecules of NH 3 ?

Moles Review cont’d 5) How much does 4.2 moles of Ca(NO 3 ) 2 weigh? 6) What is the molar mass of MgO? 7) How are the terms “molar mass” and “atomic mass” different from one another? 8)Which is a better unit for expressing molar mass, “amu” or “grams/mole”?

Stoichiometry – Where do you start? 1 st – You need a balanced equation! 2 nd – You need an amount in moles of a reactant or a product The only TRICKY part of stoichiometry is reading the problem. You will need to put everything we have learned so far together into one plan!

Balanced Equation – Read the Problem First, let’s assume that you are given an amount of a substance in grams, such as: What mass of H 2 can be prepared from the reaction of 5.00 g of Zn with HCl? Write a balanced equation and figure out what you are given and what you are solving for! (excuse my grammar) Balanced equation:

Then what? Convert this mass to moles g Zn x ____________

Then what? Multiply by the mole ratio of coefficients from the balanced equation. Just use them to convert from one chemical in the reaction to another – make sure your units cancel! 5.00 g Zn x 1 mol Zn x mol H g Zn mol Zn

Then what? Convert moles to grams since the problems asked for grams, not moles! 5.00 g Zn x 1 mol Zn x 1 mol H 2 x g H 2__ 65.41g Zn 1 mol Zn mol H 2

How did all of that go again? 1. Start with a balanced equation 2. Find within problem the amount of reactant or product given, and what you are solving for. 3. Convert given to moles 4. Use your mole ratio (coefficients from your balanced equation) 5. Convert out of moles if needed

Summarized into three steps 1. Convert to moles 2. Use the mole ratio 3. Convert out of moles

PRACTICE! PRACTICE!! How many moles of O 2 would be needed to burn g of butane (C 4 H 10 )?

Iron in the form of fine wire burns in oxygen to form iron (III) oxide. 4Fe(s) + 3O 2 (g)  2Fe 2 O 3 (s) How many moles of O 2 are needed to produce 5.21 moles of Fe 2 O 3 ?

White phosphorus, P 4 is made by fusing calcium phosphate with carbon and sand (silicon dioxide). Write the equation and determine how many grams of calcium phosphate are required to produce 5.00 g of phosphorus.