3. WHAT IS IT??
Chemists use balanced chemical equations as a
basis to calculate
A. How much reactant is needed
B. How much product is formed in a reaction.
The calculation of quantities in chemical reactions
is called Stoichiometry
stoicheion "element“
metron "measure"
4. LIKE A RECIPE
A balanced chemical equation provides the same kind of quantitative
information that a recipe does.
5. LET’S LOOK AT AN EVERYDAY EXAMPLE!
In a five day work
week, tiny tike is
scheduled to make 640
tricycles. How many
wheels should be in the
plant on Monday
morning to make those
tricycles?
6. INTERPRETING CHEMICAL EQUATIONS
A balanced chemical equation can be interpreted in terms of different
quantities, including numbers of
Representative Particles
Atoms
Molecules
Functional Units
Moles
Mass - Grams
Volume - Liters
7. INTERPRETING CHEMICAL EQUATIONS
This reaction requires the use of
a catalyst, high pressure (100–
1,000 atmospheres), and
elevated temperature (400–550
°C [750–1020 °F]).
8. USES OF AMMONIA
The major use of ammonia is as a fertilizer
Explosives (e.g., Trinitrotoluene (TNT),
nitroglycerin, and nitrocellulose)
Synthetic fibers, such as nylon and rayon
Dyeing and scouring of cotton, wool, and silk
A coolant in refrigeration and air-conditioning
equipment
Minor uses is inclusion in certain household
cleansing agents
13. WRITING AND USING MOLE RATIOS
Mole Ratios are used to convert between:
moles of reactant and moles of product
moles of reactants
moles of products
A mole ratio is a conversion factor derived from the
coefficients of a balanced chemical equation interpreted
in terms of moles.
16. PRACTICE ON YOUR OWN
Page 360 #11
11. This equation shows the formation of aluminum oxide, which
is found on the surface of aluminum objects exposed to the air.
4Al(s) + 3O2(g) 2Al2O3(s)
a. Write the six mole ratios that can be derived from this
equation.
b. How many moles of aluminum are needed to form 3.7 mol
Al2O3?
19. PRACTICE ON YOUR OWN
Page 361 # 13
13. Acetylene gas (C2H2) is produced by adding water to calcium
carbide (CaC2).
CaC2(s) + 2H2O(l) C2H2(g) + Ca(OH)2(aq)
How many grams of acetylene are produced by adding water to 5.00 g
CaC2?
20. PRACTICE ON YOUR OWN
Page 361 # 13
13. Acetylene gas (C2H2) is produced by adding water to calcium
carbide (CaC2).
CaC2(s) + 2H2O(l) C2H2(g) + Ca(OH)2(aq)
How many grams of acetylene are produced by adding water to 5.00 g
CaC2?
21. INTERPRETING CHEMICAL EQUATIONS
A balanced chemical equation can be interpreted in terms of different
quantities, including numbers of
Moles
Mass - Grams
Representative Particles
Atoms
Molecules
Functional Units
Volume - Liters
23. unit
given
unit
requested
OTHER STOICHIOMETRIC CALCULATIONS
In a typical stoichiometric problem,
given quantity is first converted to moles
mole ratio from the balanced equation is
used to calculate the number of moles of
the wanted substance
moles are converted to any other unit of
measurement related to the unit mole, as
the problem requires
26. Analyze List the knowns and the unknown.
Knowns
• mass of water 29.2 g H2O
• 2 mol H2O = 1 mol O2 (from balanced equation)
• 1 mol H2O = 18.0 g H2O (molar mass)
• 1 mol O2 = 6.02 x 1023 molecules O2
Unknown
• molecules of oxygen = ? molecules O2
The following calculations need to be done:
g H2O mol H2O mol O2 molecules O2
The appropriate mole ratio relating mol O2 to mol H2O from the
balanced equation is 1 mole O2 /2 mol H2O.
27. PRACTICE ON YOUR OWN
Page 364 # 15
15. How many molecules of oxygen are produced by the
decomposition of 6.54 g of potassium chlorate (KClO3)?
2KClO3(s) 2KCl(s) + 3O2(g)
32. LIMITING REAGENT AND EXCESS REAGENT
Limiting Reagent is the reagent that determines
the amount of product that can be formed by a
reaction
H2 + O2 H2O
O2 – Red
H2 - Blue
33. Excess Reagent- is the reagent not used up (what
is left over in a chemical reaction)
LIMITING REAGENT AND EXCESS REAGENT
37. PERCENT YIELD
The percent yield is a measure of the efficiency of a
reaction carried out in the laboratory.
Theoretical yield -maximum amount of product that could
be formed from given amounts of reactants
Actual yield the amount of product that actually forms when
the reaction is carried out in the laboratory
