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Stoichiometry“Calculating Quantities in Reactions”
Balanced Equations Show Proportions
• The coefficients in a balanced chemical equation represent the numbers of particles for each substance in the reaction.
2H2 + O2 2H2O
• For this equation, the coefficients show that _____ molecules of hydrogen react with _____ molecules of oxygen to yield _____ molecules of water.
Amounts in Moles
• Just as you can interpret these equations in terms of particles, you can interpret them in terms of moles.
• The coefficients in a balanced equation also represent the moles of each substance.
2C8H18 + 25O2 16CO2 + 18H2O
How many moles of octane react? ______________
How many moles of oxygen react? ______________
How many moles of CO2 are produced? ______________
How many moles of water are produced? ______________
Mole Ratios in a Rxn
• Stoichiometry – the proportional relationship between two or more substances during a chemical reaction.
• You will soon be able to determine how much of a product is formed from a given quantity of reactant.
• The mole ratio is the key.• The coefficients are ratios or conversion factors to convert
between reactants and products. These ratios are called MOLE RATIOS
Practice With Mole Ratios
• Consider the following reaction:• Phosphoric Acid neutralizes Barium Hydroxide ??
• What is the molar ratio of acid to base? __________. • Base to salt? __________. Acid to salt? __________. • Base to acid? __________. Water to acid? __________. • Water to base? __________. Base to water? __________.
Making Calculations
• The mole ratios are in ____________, obviously.
• You may ONLY convert between reactants and products through MOLES using the mole ratio as a conversion factor.
• Make a T-Chart and solve just as we have done in the past
Order of Operations
Grams of “A” 1 mole of “A”
Molar mass of “A”
(in grams)
# of moles of “B”
# of moles of “A” 1 mole of “B”
Molar mass of “B”(in grams)
Molar Ratio of “A” to “B”
This process enables us to convert from one reactant to another, one reactant to a product, or one product to another using the molar ratios from the balanced chemical equation.
Practice With Stoich
• How many moles of water can be produced by the combustion of 2.45 moles of propane?
Step 1: Write out the balanced reaction.
Step 2: Determine the molar ratio or the starting component and the ultimate component.
Step 3: Make a chart of relationships and solve.
Practice with Conversions
• Convert 0.85 moles of oxygen gas to grams of oxygen gas.
• Convert 12.54 grams of pentane (C5H12) to moles of pentane
Practice with Conversions
• How many grams of oxygen are required to burn 12.54 grams of pentane (C5H12) to completion?
Stoichiometry Problems
___POCl3(l) + ___H2O(l) ___H3PO4(l) + ___HCl(g)
• How many grams of hydrochloric acid will be produced from the consumption of 18.45 grams of POCl3?
Stoichiometry Problems
1 POCl3(l) + 3 H2O(l) 1 H3PO4(l) + 3 HCl(g)
• How many grams of hydrochloric acid will be produced from the consumption of 18.45 grams of POCl3?
• How many grams of phosphoric acid will be produced with this quantity of POCl3?
More Practice
What volume of H3PO4 forms when 56 mL POCl3 completely react? (density of POCl3 = 1.67 g/mL; density of H3PO4 = 1.83 g/mL)
1 POCl3(l) + 3 H2O(l) 1 H3PO4(l) + 3 HCl(g)
Using Molecules
How many grams of C5H8 form from 1.89x1024 molecules C5H12? C5H12(l) C5H8(l) + 2H2(g)
• Get started on your homework
packet “Calculating Quantities
in Reactions”
• This will be homework and
is due tomorrow