Transcript Stoichiometry

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
223.40g/mol + 96.00g/mol =
319.40g/mol

159.70g/mol × 2
= 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