Stoichiometry
brought to you by
The Gruffalo
narrated by Mr. Arcuri
The Reactants:
terrible tusks - Tt
knobby knees - Kk
orange eyes - Oe
terrible claws - Tc
turned out toes - Tot
black tongue - Bt
terrible teeth - Tth
poisonous wart - Pw
purple prickles - Pp
The Reactions:
2Tt + 8Tth + 1Pw + 2Oe + 1Bt
2Kk + 10Tot + 27Pp + 10Tc
1 head + 1 body
1 head
1 body
Gruffalo
1. How many heads will 4 Oe make? __________
2. How many terrible tusks (Tt) are required to make 4 bodies? _________
3. How many knobby knees (Kk) are required to react with 61 purple prickles?
4. How many turned out toes (Tot) are required to make 8.31 bodeis?
5. How many Gruffalos can be made with 85.2 Kg of black tongues? If 1 black
tongue has a mass of 3.2kg.
Stoichiometry with moles
Introduction
The word stoichiometry derives from two Greek words: stoicheion (meaning "element")
and metron (meaning "measure"). Stoichiometry deals with calculations about the
masses (sometimes volumes) of reactants and products involved in a chemical reaction.
The most common stoichiometric problem will present you with a certain amount of a
reactant and then ask how much of a product can be formed. Here is a generic chemical
equation:
2A + 2B → 3C
Here is a typically worded problem: Given 20.0 grams of A and sufficient B, how
many grams of C can be produced?
You will need to use molar ratios, molar masses, balancing and interpreting equations,
and conversions between grams and moles.
Examples
If 6 moles of Cl2(g) can react with 3 moles of Na
a. How many moles of Cl2(g) will react with 6 moles of Na? ___________
b. How many moles of Cl2(g) will react with 1 mole of Na? ___________
c. How many moles of Na does it take to react with 8 moles of Cl2(g)? _____
This is stoichiometry! You are using mole ratios to determine specific amounts.
Sec 7.1 – The Meaning of the Coefficients in a Balanced Equation
Can be summed up in two words – MOLAR RATIOS
Here’s an example;
2 H2 + O2 → 2 H2O
What is the molar ratio between H2 and O2? _________
What is the molar ratio between O2 and H2O? _________
What is the molar ratio between H2 and H2O? _________
the coefficients of a reaction only give the ratio in which substances react
Stoichiometry Calculations
There are many types of calculations. For EVERY type of calculation, moles must be
calculated. This is called the mole bridge. The first type of problem is called Mole to
Mole.
1. Mole to Mole Calculations
Set up a ratio and solve for the unknown
Example 1.
N2 + 3 H2 ---> 2 NH3
a. How many moles of N2 are required to react with 15 moles of H2?
b. How many moles of NH3 are produced when 18.0 moles of H2 are reacted?
Example 2. Al2(CO3)3 + 3CaCl2  3CaCO3 + 2AlCl3
a. How many moles of AlCl3 would be produced if 6 moles of CaCl2 reacted with
Al2(CO3)3
Given : 6 moles of CaCl2
Find : moles of AlCl3
b. How many moles of AlCl3 would be produced if 13.4 moles of CaCl2 reacted
c. How many moles of CaCO3 would be produced if 6.7 moles of CaCl2 reacted
Stoichiometry Calculations
- Mass to Mole or Mole to Mass Calculations Chapter 5 Review: Mass and Moles
1) How many moles of Na(CO3)2 are in 256g of Na(CO3)2?
2) 0.450 gram of Fe contains how many moles of Fe?
Mole and Mass Calculations
You must always go to moles first – then convert using the ratio.
1. How many moles of O2 gas will be produced by the decomposition of 27.0g of HgO.
2HgO → O2 + 2Hg
Also knowing the how much product you want to get – you can determine
the amount of reactant.
2. How many grams of KClO3 must be decomposed to produce 1.45 mole of O2 ?
2KClO3 → 3O2 + 2KCl
Here's the equation to use for all three problems:
2 H2 + O2 → 2 H2O
1. How many grams of H2O are produced when 2.50 moles of oxygen are used?
2. If 3.00 moles of H2O are produced, how many grams of oxygen must be consumed?
3. How many grams of hydrogen gas must be used, given the data in problem two?
4. Powder Zinc metal reacts violently with sulphur (S8) when heated to produce zinc
sulphide. 8Zn + S8 → 8ZnS
What is the amount of moles of S8 required to react with 25.0 g of Zn?
5. Aluminium oxide is decomposed using electricity to produce aluminium metal and
oxygen.
write a balanced equation
How many moles of Al can be produced from 125g of aluminium oxide?
Stoichiometry Calculations - Mass to Mass Calculations
The balanced equation gives the mole ratio of the reactants and products. But in a lab it
impossible to weight “moles of a reactant” so grams are used. Therefore you must
calculate the amount of grams of product from a certain mass of reactant
How many grams of KCl, are produced by decomposing 118g KClO3?
Problem; there is no direct relationship form g → g, therefore you must go to moles
because you can use the ratio to find a relationship between moles, mol → mol
The only difference from yesterday is that you must add 1 step at the beginning and the
end to convert whatever you are calculating from g → mol or mol → g
2KClO3 → 2KCl + 3O2
118g KClO3
118g KClO3 → mol KClO3
? g KCl
mol KCl → ? g KCl
118g KClO3 → mol KClO3 → RATIO → mol KCl → ? g KCl
How many grams of O2 will be required to react with 14.6 g Na to form
Na2O?
4Na + O2 → 2Na2O
14.6g Na → ? g O2
14.6g Na → mol Na →→→→mol O2 → ? g O2
14.6g Na → mol Na → RATIO →mol O2 → ? g O2
A propane stove produces heat by combustion of propane (C3H8) in oxygen.
Write a balanced equation for this reaction
Determine the mass of O2 required to completely burn 10.0g of propane.
Sodium reacts with Oxygen to produce sodium oxide.
Write a balanced equation for this reaction
Calculate the number of grams of sodium Oxide that will be produced when 115g of
sodium react with oxygen.
Pg 124 # 1-5, 6ab, 7ab