Chemistry chapter 9

Mass to Mass and Limiting Reactants

I. Coefficients represent moles of formula units (compound units, molecules, etc.).

The coefficients show the mole ratio that reactants combine and products are produced. The compounds must always combine or be produced in this ratio - they will not combine or be produced in any other ratio.

II. Mass to Mass

A. Mass to mass problems involve using the mole ratio from the balanced equation to predict:
1. how much product can be made from a specified amount of reactant.

2. how much reactant is needed to form a specified amount of product.

3. how much reactant is needed to react with a specified amount of another reactant.

4. how much product can be made at the same time as a specified amount of another product.

B. Steps to solve a mass to mass problem

1. HAVE A BALANCED EQUATION WITH THE CORRECT FORMULAS!

2. Convert grams of the given compound to moles

3. Use the mole ratio from the balanced equation to predict how many moles of the unknown

can be made or are needed

4. Convert the moles of the unknown found above to grams

III. Limiting Reactants

1. if one of the reactants is less than the needed mole ratio amount (as determined by the balanced equation), it will limit, or directly determine, how much product can actually be produced

B. Solving a limiting reactant problem is solving two mass-to-mass problems and comparing the two answers.

1. Using reactant X, solve a mass-to-mass problem starting with reactant X to determine how much of the identified product reactant X could make.

2. Using reactant Z, solve a mass-to-mass problem starting with reactant Z to determine how much of the identified product reactant Z could make.

3. The reactant that could make the SMALLEST amount of product is called the limiting reactant, and the amount of product it makes is the most that can be made. This is called the theoretical yield.

IV. Percent yield: