StoichiometryStoichiometry

mass and amount mass and amount relationships between relationships between

reactants and products in reactants and products in a chemical reaction a chemical reaction

Rules for Solving Rules for Solving Stoichiometry ProblemsStoichiometry Problems

1.1. A balanced, properly written A balanced, properly written equation is essential because the equation is essential because the coefficients tell you the mole to coefficients tell you the mole to mole ratio.mole ratio.

2.2. Converting to moles is essential!Converting to moles is essential!

ExampleExample: When CaC: When CaC22 reacts with reacts with water, acetylene gas (Cwater, acetylene gas (C22HH22) and ) and calcium hydroxide are produced. How calcium hydroxide are produced. How many grams of water are required to many grams of water are required to produce 1.55 moles of Cproduce 1.55 moles of C22HH22??

Step 1Step 1: Write a balanced equation.: Write a balanced equation.

CaCCaC22 + 2H + 2H22O O C C22HH22 + Ca(OH) + Ca(OH)22

Step 2Step 2: Determine what info you have : Determine what info you have and what you are trying to determine.and what you are trying to determine.

You know you need to produce 1.55 You know you need to produce 1.55 moles of Cmoles of C22HH22, and you need to , and you need to determine how many grams of water determine how many grams of water are required to do this.are required to do this.

Step 3Step 3: What is the mole to mole ratio : What is the mole to mole ratio between the two? HINT! You between the two? HINT! You determine this using the coefficients determine this using the coefficients from the from the balancedbalanced equation equation..

moles of Cmoles of C22HH22 : moles of H : moles of H22OO

1:2 1:2

Step 4Step 4: Apply the ratio to determine : Apply the ratio to determine how many moles of water will be how many moles of water will be required.required.

1.55 mol C1.55 mol C22HH22 xx 2 mol H2 mol H22OO == 3.10 3.10 mol Hmol H22OO

11 1 mol C1 mol C22HH22

Step 5Step 5: The question asks for grams of : The question asks for grams of HH22O, so convert 3.10 mol of HO, so convert 3.10 mol of H22O to O to grams.grams.

3.10 mol H3.10 mol H22OO x x 18.0 g18.0 g = = 55.8 g 55.8 g HH22OO

11 1 mol H 1 mol H22OO

REMEMBER! The ratio REMEMBER! The ratio supplied by the coefficients supplied by the coefficients of the balanced equation is of the balanced equation is

a a molemole toto molemole ratio! It ratio! It does not apply to grams!does not apply to grams!

Stoichiometry PracticeStoichiometry Practice

1. Determine the mass of lithium 1. Determine the mass of lithium hydroxide produced when 3.80 hydroxide produced when 3.80 moles of lithium nitride reacts moles of lithium nitride reacts with water according to the with water according to the following equation:following equation:

LiLi33N + 3HN + 3H22O O NH NH33 + 3LiOH + 3LiOH

2. What mass of sodium chloride is 2. What mass of sodium chloride is produced when 0.45 g of chlorine produced when 0.45 g of chlorine reacts with excess sodium iodide?reacts with excess sodium iodide?