Objectives

• SWBAT define stoichiometry.• SWBAT write a mole ratio relating two

substances in a chemical reaction.• SWBAT calculate the mass of a reactant

or product from the mass of a different reactant or product.

Stoichiometry

What is Stoichiometry?

• “To measure elements”• The study of the quantitative relationship

between the amounts of reactants and products in a chemical reaction.

• A balanced chemical equation can be interpreted in terms of particles, mass, and moles.

To make a bike?

iron + oxygen iron (III) oxide

What is the balanced chemical equation?

What does this tell us?

Iron + Oxygen Iron (III) Oxide

4 Fe + 3 O2 2Fe2O3

4 atoms Fe + 3 molecules O2

2 formula units Fe2O3

4 moles Fe + 3 moles O2 2 moles Fe2O3

55.85g/mol × 4 = 223.40 g/mol

+ 32.00g/mol × 3 = 96.00g/mol

159.70g/mol × 2 = 319.40g/mol

223.40g/mol + 96.00g/mol = 319.40g/mol

319.40g/mol

Mole Ratios

• Solving any reaction stoichiometry problem involves the use of a mole ratio

• A mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction

• This information is obtained directly from the coefficients in a balanced chemical equation

Mole Ratios – Examples

• Consider the following equation:

2 H2 + O2 → 2 H2O

• sample mole ratios:– 2 mol H2 = 2 mol H2O

– 1 mol O2 = 2 mol H2O

– 2 mol H2 = 1 mol O2

Sample Problem #1

Potassium and water react to form potassium hydroxide and hydrogen gas. How many moles of hydrogen are produced when 0.04 moles of potassium are used?

Answer

• 0.02 mol H2

Sample Problem #2

• Ammonium nitrate, an important fertilizer, produces dinitrogen monoxide and water when it decomposes. Determine the mass of the water produced from the decomposition of 25.0 g of ammonium nitrate.

Answer

• 11.2 g H2O

Answer

• 2.0 x 10 24 formula units of NaCl

Announcement!

• Please remove your wonderful STEM posters by next Wednesday.

Agenda

• Practice Problems• Stoichiometry Worksheets

Homework

• Stoichiometry Mole to Mole Probs• Stoichiometry Mass to Mass Probs• Stoichiometry Volume to Volume Probs

Drill 3/6/14

• List the number of conversion factors and type for mole-to-mole AND mass-to-mass conversion stoichiometry problems.

Drill 3/6/14• Conversion factors/type for mole-to-mole

AND mass-to-mass conversion problems.

• Mole-to-mole – 1 conversion factor = mole ratio (use coefficients of “given” and “TBD”

• Mass-to-mass – 3 conversion factors = 1. Formula mass

2. Mole ratio

3. Formula mass

Homework Due – questions??

• 11-2 Practice Probs WS – front side only• Stoichiometry Practice #3

Practice Problem

• How many grams of water are produced when 7.00 grams of oxygen (O2) react with an excess of hydrogen according to the reaction shown below?

2 H2 + O2 → 2 H2O

Answer

• 7.89 g water

Practice Problems

• Laughing gas (N2O) is sometimes used as anesthetic in dentistry. It is produced when ammonium nitrate is decomposed according to the following reaction:

NH4NO3 (s) → N2O (g) + 2 H2O (l)

• How many moles of NH4NO3 are required to produce 33.0 g N2O?

Answer

• 0.750 mol NH4NO3

Practice Problem

• Acetylene gas (C2H2) is produced as a result of the following reaction:

CaC2 + 2 H2O → C2H2 + Ca(OH)2

• If 32.0 g of CaC2 are consumed in this reaction, how many grams of water are needed?

Answer

• 18.0 g water

Practice Problem

• Milk of magnesia, a suspension of Mg(OH)2 in water, reacts with stomach acid, HCl, in a neutralization reaction:

Mg(OH)2 + 2 HCl → 2 H2O + MgCl2

• How many formula units of MgCl2 will be produced if 3.00 g of Mg(OH)2 reacts?

Drill #13 2/27 & 28/13

• For the balanced equation shown below, how many moles of H2 can be produced by 0.6351 moles of Al?

• mole to mole conversion

2 Al + 6 HCl → 2 AlCl3 + 3 H2

Answer

• 0.9527 mol H2

Drill #14 3/1 & 3/4/13

• Complete Empirical and Molecular Formula Drill

Objectives

• SWBAT define stoichiometry.• SWBAT write a mole ratio relating two

substances in a chemical reaction.• SWBAT calculate the mass of a reactant

or product from the mass of a different reactant or product.

Answer

• 3.10 x 1022 formula units MgCl2

Drill # 2/26/14

• Nitrogen and hydrogen react to form ammonia. How many grams of hydrogen are needed to react with 50.0 g of nitrogen in this reaction?

• Mass to mass conversion

Answer

• 10.7 g H2