Chapter 9
Stoichiometric Problems
It is important to recognize that the coefficients in a balanced equation gives us the relative numbers of molecules
*A balanced equation relates the numbers of molecules of reactants and products. It can also be expressed in terms of the numbers of moles of reactants and products.
*In stoichiometry, always make sure the equation is balanced before continuing the problem
*ask the questions: Is it the right compound? and Is it the right unit? to make sure you are on the right track
*The process of using a chemical equation to calculate the relative amounts of reactants and products involved in the reaction is called doing stoichiometric calculations. To convert between moles of reactants and moles of products, we use mole ratios derived from the balanced equation.
Limiting Reagent Problems
*To determine how much product can be formed from a given mixture of reactants, we have to look for the reactant that is limiting - the one that runs out first thus limits the amount of product that can form
*The reactant that runs our first and thus limits the amounts of products that can form is called the limiting reactant
*The chemical equation indicates the relative numbers of reactant and product molecules involved in the reaction
*using the equation permits us to determine the amounts of reactants needed to give a certain amount of product or to predict how much product we can make from the given quantity of reactants
*we can use an equation to predict the moles of products that a given number of moles of reactants will yield
*moles represent number of molecules
*Steps for solving stoichiometry problems involving limiting reactants
1.Write and balance the equation for the reaction
2.convert known masses of reactants to moles
3.using the numbers of moles of reactants and the appropriate mole ratios, determine which reactant is limiting
4.using the amount of the limiting reactant and the appropriate mole ratios, compute the number of moles of the desired product
5.convert from moles of product to grams of product, using the molar mass (if this is required by the problem)
Identifying Limiting and Excess Reagents
*The reactant that runs our first and thus limits the amounts of products that can form is called the limiting reactant
*The reactant that is greater (bigger than the limiting) is usually the excess reactant.
*The compound that will be in excess after a reactions is the excess reactant.
Percent Yield problems.
*The theoretical yield is the amount of product predicated from the amounts of the reactants used.
*The actual yield of the product, which is the amount of product actually obtained, is often compared to the theoretical yield
this comparison, expressed as a percentage, is the percent yield
*Formula: actual/theoretical X 100%
*A balanced equation relates the numbers of molecules of reactants and products. It can also be expressed in terms of the numbers of moles of reactants and products
*The process of using a chemical equation to calculate the relative amounts of reactants and products involved in the reaction is called doing stoichiometric caluclations. to convert between moles and tractants and moles of products, we use mole ratios derived from the balanced equation
often reactants are not “mixed” in stoichiometric problems
It is important to recognize that the coefficients in a balanced equation gives us the relative numbers of molecules
*A balanced equation relates the numbers of molecules of reactants and products. It can also be expressed in terms of the numbers of moles of reactants and products.
*In stoichiometry, always make sure the equation is balanced before continuing the problem
*ask the questions: Is it the right compound? and Is it the right unit? to make sure you are on the right track
*The process of using a chemical equation to calculate the relative amounts of reactants and products involved in the reaction is called doing stoichiometric calculations. To convert between moles of reactants and moles of products, we use mole ratios derived from the balanced equation.
Limiting Reagent Problems
*To determine how much product can be formed from a given mixture of reactants, we have to look for the reactant that is limiting - the one that runs out first thus limits the amount of product that can form
*The reactant that runs our first and thus limits the amounts of products that can form is called the limiting reactant
*The chemical equation indicates the relative numbers of reactant and product molecules involved in the reaction
*using the equation permits us to determine the amounts of reactants needed to give a certain amount of product or to predict how much product we can make from the given quantity of reactants
*we can use an equation to predict the moles of products that a given number of moles of reactants will yield
*moles represent number of molecules
*Steps for solving stoichiometry problems involving limiting reactants
1.Write and balance the equation for the reaction
2.convert known masses of reactants to moles
3.using the numbers of moles of reactants and the appropriate mole ratios, determine which reactant is limiting
4.using the amount of the limiting reactant and the appropriate mole ratios, compute the number of moles of the desired product
5.convert from moles of product to grams of product, using the molar mass (if this is required by the problem)
Identifying Limiting and Excess Reagents
*The reactant that runs our first and thus limits the amounts of products that can form is called the limiting reactant
*The reactant that is greater (bigger than the limiting) is usually the excess reactant.
*The compound that will be in excess after a reactions is the excess reactant.
Percent Yield problems.
*The theoretical yield is the amount of product predicated from the amounts of the reactants used.
*The actual yield of the product, which is the amount of product actually obtained, is often compared to the theoretical yield
this comparison, expressed as a percentage, is the percent yield
*Formula: actual/theoretical X 100%
*A balanced equation relates the numbers of molecules of reactants and products. It can also be expressed in terms of the numbers of moles of reactants and products
*The process of using a chemical equation to calculate the relative amounts of reactants and products involved in the reaction is called doing stoichiometric caluclations. to convert between moles and tractants and moles of products, we use mole ratios derived from the balanced equation
often reactants are not “mixed” in stoichiometric problems
This website explains the chemical equation, balancing chemical equations, the mole, limiting and excess reagents, percent composition, and empirical formula.
This website explains stoichiometry, molar mass, and percent mass.
This video helps show how to do basic stoichiometric problems.
This video includes how to solve limiting reagent problems and identifying limiting and excess reagents.
This video includes how to solve percent yield problems.
This is a website that has practice problems dealing with stoichiometry.
This is a worksheet with identifying limiting and excess reagents and limiting reactant problems.
This is a website with percent yield practice problems that allows you to check your answers.