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)

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packet “Calculating Quantities

in Reactions”

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