Chemical Equations and Stoichiometry

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Chemical Equations and Stoichiometry
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Chemical Equations

• Methane reacts with oxygen to form carbon dioxide
  and water

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Indicate the physical states of the matter
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Balancing Chemical Equations
SO2(g) O2(g) ? SO3(g)
P2O5(s) H2O(l) ? H3PO4(aq)
CH4(g) Cl2(g) ? CCl4(l) HCl(g)
Al4C3(s) H2O(l) ? Al(OH)3(s)
CH4(g)
C4H10O(l) O2(g) ? CO2(g)
H2O(g)
Fe(OH)3(s) H2SO4(aq) ?
Fe2(SO4)3(aq) H2O(l)
Mg3N2(s) H2SO4(aq) ? MgSO4(aq)
(NH4)2SO4(aq)
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Chemical Reactions

• To be correct, the equation that represents a
  chemical reaction must conserve both mass and
  charge, i.e., it must be balanced.
• Chemical reactions fall into two major
  categories
• Electron transfer change in oxidation state of
  one or more elements in the reaction. Called
  reduction and oxidation Called Redox reactions
• No electron transfer No change in oxidation
  state.
• Types of Reactions - Part I.
• Combination Reactions
• Decomposition Reactions
• Combustion Reactions

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• Elemental Combination (redox) Two or more
  substances react to form one product.

• For prediction purposes, the positive oxidation
  state species is usually in the product and is
  usually in the highest positive oxidation state
  for that element sulfur (S) is an exception.
• Decomposition Reactions One reactant reacts to
  produce two or more products (the reverse of
  combination rxns).

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• Combustion Reactions Normally involve reaction
  with O2(g). We have seen several metals react
  with oxygen in the elemental combination
  reaction. Hydrocarbons react with oxygen to from
  carbon dioxide gas and liquid water.

a. C5H12(l) O2 ---gt
b. C4H10(l) O2(g) ---gt
c. CO(g) O2(g) ---gt
d. B2H6(g) O2(g) ---gt
e. CH3OH(l) O2(g) ---gt
f. CH4(g) O2(g) ---gt
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Patterns of Chemical Reactivity
Write a balanced equation for the reaction that
occurs when
(a) aluminum metal undergoes a combination
reaction withbromine liquid
(b) strontium carbonate decomposes into strontium
oxide and carbon dioxide when heated
(c) heptane liquid burns in air
(d) dimethylether, CH3OCH3(g), is combusted in air
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Calculations Based Upon Chemical Equations

1. Develop an equation that represents the reaction
2. Balance the equation
3. Calculate the molar mass of each component in the
   equation
4. Note the densities of all neat liquids and the
   concentrations of allsolutions used in the
   reaction
5. Enter given quantities into a table below the
   equation
6. Convert neat liquid volumes to masses using
   densities
7. Convert masses to moles using molar masses
8. Convert solution volumes to moles using
   concentrations
9. Divide each mole quantity by its stoichiometric
   coefficient
10. Determine the limiting reagent and moles of
    product
11. Determine masses and volumes of products a
    appropriate

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Calculations Based Upon Chemical Equations
Calcium hydride reacts with water to form calcium
hydroxide and hydrogen gas. How many grams of
calcium hydride are needed to form 5.0 g of
hydrogen?




Molarity




density
Molar Mass(g/mole)
42.0938
18.0152
74.0926
2.0158
CaH2(s) H2O(l) ? Ca(OH)2(aq)
H2(g)
2
2




volume
?
52.2 g
mass
5.0 g
2.4804 mol
moles
1.2402 mol
1.2402
1.2402
L.R.
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Detonation of nitroglycerin liquid, C3H5N3O9(l),
produces carbon dioxide gas, nitrogen gas,
oxygen gas, and gaseous water. (a) Write a
balanced equation for this process. (b) If a
sample containing 3.00 ml of nitroglycerin
(density 1.592 g/ml) is detonated, how many
total moles of gas are produced? (c) If each
mole of gas occupies 55 L under the conditions
of the explosion, how many liters of gas are
produced? (d) How many grams of nitrogen gas are
produced in the detonation?
(a) 4 C3H5N3O9(l) ? 12 CO2(g) 6 N2(g) 10
H2O(g)
(b) 0.152 mol gas
(c) 8.4 L gas
(d) 0.884 g N2
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Limiting Reagents
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One of the steps in the commercial process for
converting ammonia to nitric acid is the
conversion of NH3 to NO
In a certain experiment, 2.25 g of NH3 reacts
with 3.75 g of O2.

1. How many grams of NO form?
2. How many grams of the excess reactant remain
   after the limitingreactant is completely
   consumed?

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Chemical Equations and Chemical Analysis
Analytical chemists use a variety of
approachesto identify substances as well as to
measure thequantities of components of
mixtures. Modern analytical chemistry utilizes
instruments,in addition to chemical reactions
and stoichiometry to analyze mixtures.
Quantitative Analysis of a Mixture
A substance, present in unknown
amount can be allowed to react with a
known quantity of another substance.
If the stoichiometric ratio for their reaction is
known, the unknown amount can be determined. A
material of an unknown composition can be
converted to one or more known substances, whose
amounts can be determined and related to the
amount of the original substance.
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CH3CO2H(aq) NaOH(aq) --gt CH3CO2Na(aq)
H2O(l)
Na2SO4(aq) BaCl2(aq) --gt BaSO4(s) 2
NaCl(aq)
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Empirical Formulas

• whole number ratio of the elements in a compound

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Determine the empirical formulas of the compounds
with the following composition by mass
10.4 C, 27.8 S, and 61.7 Cl
(a)
(b)
21.7 C and 68.7 F
(c)
32.79 Na, 13.02 Al, and 54.19 F
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The characteristic odor of pineapple is due to
ethyl butyrate, a compound containing carbon,
hydrogen, and oxygen. Combustion of 2.78 mg of
ethyl butyrate produces 6.32 mg of CO2 and 2.58
mg of H2O. What is the empirical formula of the
compound?
44.0103 g/mol
18.0152 g /mol
CxHyOz O2 ? CO2
H2O
6.32 mg
2.78 mg
2.58 mg
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C3H6O