Chemical Reactions and Equations Stoichiometry Goals: 1. Mole ...
Chemical Reactions and Equations Stoichiometry Goals: 1. Mole Relationships Define and recognize the mole ratio in a balanced equation as a conversion factor for solving stoichiometry problems.
2. Ideal Stoichiometry Calculations Demonstrate solutions to problems involving conversions between the units of moles, grams and liters.
3. Limiting Reactants and Percent Yield “Real world” stoichiometry. Explain and use the concepts of limiting reagent and percent yield to predict product quantities and evaluate lab work.
Reaction Stoichiometry Reaction Stoichiometry measures the quantitative relationships among substances as they participate in chemical reactions. These quantitative relations in calculations are used to determine the amount of products/reactants that are produced/needed in a given reaction.
Types of Reaction Stoichiometry Problems Problem types are determined by the given and unknown units of the reactants or products
Mole to Mole Mole to Mass or Mass to Mass Volume to Volume
Mass to Mole
Steps to Follow for Solving Reaction Stoichiometry Problems 1. Must have a balanced chemical equation 2. Identify given and unknown by units and chemical formula 3. Recognize that the coefficients in the balanced equation give the mole ratios that can be used for a units conversion. 4. Complete conversion steps The Mole relationship (coefficients) is ONLY relationship you know between reactants and products. Therefore you have to go through moles!
Solve the following stoichiometry mole – mole problems The coefficients give you the direct relationship.
1)
Use this equation:
2KClO3 →
2KCl
+ 3O2
How many moles of oxygen are produced by the decomposition of 6.0 moles of potassium chlorate, KClO3?
2)
Use this equation:
K3PO4 + Al(NO3)3 → 3KNO3 + AlPO4
How many moles of potassium nitrate are produced when 2.5 moles of potassium phosphate react?
Solve the following moles – grams or grams – moles problems: Given in moles
Unknown in Moles
Unknown in Grams
1) Acetylene gas, C2H2, is used in welding, produces an extremely hot flame when it burns in pure oxygen according to the following reaction.
2 C2H2(g) + 5O2(g)
4CO2(g) +
2H2O(g)
How many moles of water are produced when 25.0 grams of C2H2 burns completely?
2) Use the following equation:
3 Mg + Fe2O3 2 Fe + 3 MgO
How many moles of iron are produced with 25.0 grams of magnesium, Mg?
Solve the following stoichiometry grams-grams problems: These are the most common problem types because grams are the practical unit for lab work. Here is a road map
1) Using the following equation:
2 NaOH +
H2SO4 2 H2O +
Na2SO4
How many grams of sodium sulfate will be formed if you start with 200.0 grams of sodium hydroxide and you have an excess of sulfuric acid?
Next stoichiometry grams-grams problem type Keep this in mind: when doing stoichiometry problems, people are frequently worried by statements such as “if you have an excess of (compound X)”. What this statement means is that this isn’t a limiting reagent problem, so you can totally ignore whatever reagent you have an excess of. Think: cooking recipes – the ingredient you have too much of does not impact what you can make today.
2) Using the following equation:
Pb(SO4)2 +
4 LiNO3
Pb(NO3)4 +
2 Li2SO4
How many grams of lithium nitrate will be needed to make 250.0 grams of lithium sulfate, assuming you have an adequate amount of lead (IV) sulfate to do the reaction?
Stoichiometry When Reactants and/or Products are Gases
Reaction Stoichiometry Gas Volumes at STP Recall: STP is Standard Temperature and Pressure 0oC or 273K at 1 ATM Molar Volume of a Gas at STP : 1 mole of any gas occupies a volume of 22.4L How to Solve: The key point to look for is the conditions of temperature and pressure. If they remain constant, you may treat the volumes in the same manner you treat moles. This is because, under conditions of constant T and P, the volumes are directly proportional to the moles. Therefore we can solve volume to volume problems just like mole – mole problems. If liters at STP are used you must convert to moles. Solve the Following: 1) The equation for the combustion of methane is: CH4 +
2O2 --->
2H2O +
CO2
If 50.0 L of methane at STP are burned, what volume of carbon dioxide will be produced at STP?
Reaction Stoichiometry Gas Volumes at STP next problem type
2) Given the following equation:
C(s) +
2H2(g)
--->
CH4(g)
How many liters of hydrogen are needed to produce 20.0 L of methane?
2. Ideal Stoichiometry Calculations Demonstrate solutions to problems involving conversions between the units of moles, grams and liters.
3. Limiting Reactants and Percent Yield “Real world” stoichiometry. Explain and use the concepts of limiting reagent and percent yield to predict product quantities and evaluate lab work.
Reaction Stoichiometry Reaction Stoichiometry measures the quantitative relationships among substances as they participate in chemical reactions. These quantitative relations in calculations are used to determine the amount of products/reactants that are produced/needed in a given reaction.
Types of Reaction Stoichiometry Problems Problem types are determined by the given and unknown units of the reactants or products
Mole to Mole Mole to Mass or Mass to Mass Volume to Volume
Mass to Mole
Steps to Follow for Solving Reaction Stoichiometry Problems 1. Must have a balanced chemical equation 2. Identify given and unknown by units and chemical formula 3. Recognize that the coefficients in the balanced equation give the mole ratios that can be used for a units conversion. 4. Complete conversion steps The Mole relationship (coefficients) is ONLY relationship you know between reactants and products. Therefore you have to go through moles!
Solve the following stoichiometry mole – mole problems The coefficients give you the direct relationship.
1)
Use this equation:
2KClO3 →
2KCl
+ 3O2
How many moles of oxygen are produced by the decomposition of 6.0 moles of potassium chlorate, KClO3?
2)
Use this equation:
K3PO4 + Al(NO3)3 → 3KNO3 + AlPO4
How many moles of potassium nitrate are produced when 2.5 moles of potassium phosphate react?
Solve the following moles – grams or grams – moles problems: Given in moles
Unknown in Moles
Unknown in Grams
1) Acetylene gas, C2H2, is used in welding, produces an extremely hot flame when it burns in pure oxygen according to the following reaction.
2 C2H2(g) + 5O2(g)
4CO2(g) +
2H2O(g)
How many moles of water are produced when 25.0 grams of C2H2 burns completely?
2) Use the following equation:
3 Mg + Fe2O3 2 Fe + 3 MgO
How many moles of iron are produced with 25.0 grams of magnesium, Mg?
Solve the following stoichiometry grams-grams problems: These are the most common problem types because grams are the practical unit for lab work. Here is a road map
1) Using the following equation:
2 NaOH +
H2SO4 2 H2O +
Na2SO4
How many grams of sodium sulfate will be formed if you start with 200.0 grams of sodium hydroxide and you have an excess of sulfuric acid?
Next stoichiometry grams-grams problem type Keep this in mind: when doing stoichiometry problems, people are frequently worried by statements such as “if you have an excess of (compound X)”. What this statement means is that this isn’t a limiting reagent problem, so you can totally ignore whatever reagent you have an excess of. Think: cooking recipes – the ingredient you have too much of does not impact what you can make today.
2) Using the following equation:
Pb(SO4)2 +
4 LiNO3
Pb(NO3)4 +
2 Li2SO4
How many grams of lithium nitrate will be needed to make 250.0 grams of lithium sulfate, assuming you have an adequate amount of lead (IV) sulfate to do the reaction?
Stoichiometry When Reactants and/or Products are Gases
Reaction Stoichiometry Gas Volumes at STP Recall: STP is Standard Temperature and Pressure 0oC or 273K at 1 ATM Molar Volume of a Gas at STP : 1 mole of any gas occupies a volume of 22.4L How to Solve: The key point to look for is the conditions of temperature and pressure. If they remain constant, you may treat the volumes in the same manner you treat moles. This is because, under conditions of constant T and P, the volumes are directly proportional to the moles. Therefore we can solve volume to volume problems just like mole – mole problems. If liters at STP are used you must convert to moles. Solve the Following: 1) The equation for the combustion of methane is: CH4 +
2O2 --->
2H2O +
CO2
If 50.0 L of methane at STP are burned, what volume of carbon dioxide will be produced at STP?
Reaction Stoichiometry Gas Volumes at STP next problem type
2) Given the following equation:
C(s) +
2H2(g)
--->
CH4(g)
How many liters of hydrogen are needed to produce 20.0 L of methane?
