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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