chapter 3 - stoichiometry it is important to be able to quantify the amount of reagent(s) that will...
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Chapter 3 - Stoichiometry
It is important to be able to quantify the amount of reagent(s) that
will be needed to produce a given amount of product(s). The science of
quantifying substances involved in chemical reactions is called
Stoichiometry.
Writing Chemical Equations
• The Basics of Writing Reactionso An arrow is used to indicate reaction progress.o Reactants on the left, products on the right.o Use a ‘+’ sign between reagents and products.o Use a subscript to indicate the state of
substances.
Writing Chemical Equations
• The Basics of Writing Reactionso How can you predict the state of a substance in a
chemical reaction?o Use your knowledge of chemistry
o Covalent compounds are usually gases.o If an ionic compounds reacts with another ionic
compound, then they must be aqueous.o Water is a liquid unless the reaction produces a lot of
heat.
Writing Chemical Equations
• The Basics of Writing Reactionso Coefficients are whole numbers in front of
substances to indicate the number of particles present in the reaction.
Writing Chemical Equations
• Balancing Chemical Reactionso Use coefficients to follow the Law of Conservation
of Mass
__Na2S(aq) + __BaNO3(aq) __NaNO3(aq) + __BaS(s)
__C8H18(g) + __O2(g) __H2O(g) + __CO2(g)
Writing Chemical Equations
• Balancing Chemical Reactionso Write the following chemical reactions then
balance them;o Iron reacts with oxygen gas to produce iron(III) oxide.
o Electricity can break down water into oxygen gas and hydrogen gas by a process called electrolysis.
Writing Chemical Equations
• Balancing Chemical Reactionso Write the following chemical reactions then
balance them;o Ethane reacts with oxygen gas to produce water vapor
and carbon dioxide.
o Calcium nitrate and lithium chloride react to produce soluble lithium nitrate and a white precipitate called calcium chloride.
Writing Chemical Equations
• Simple Chemical Reactionso Synthesis (Combination) Reactions;
o When two atoms or molecules combine to form a larger compound.
N2(g) + 3H2(g) 2NH3(g)
Writing Chemical Equations
• Simple Chemical Reactionso Synthesis (Combination) Reactions;
o Write the chemical reaction in which sodium metal reacts with oxygen gas.
Writing Chemical Equations
• Simple Chemical Reactionso Decomposition Reactions;
o A compound breaks apart into two smaller molecules or atoms;
2H2O2(l) 2H2O(g) + O2(g)
Writing Chemical Equations
• Simple Chemical Reactionso Decomposition Reactions;
o Write the decomposition of carbonic acid into water and carbon dixoide;
Writing Chemical Equations
• Simple Chemical Reactionso Combustion Reactions;
o Combustion occurs when oxygen gas is consumed in a chemical reaction and is combined to all products.
Writing Chemical Equations
• Simple Chemical Reactionso Combustion Reactions;
o Combustion occurs when oxygen gas is consumed in a chemical reaction and is combined to all products.
Writing Chemical Equations
• Simple Chemical Reactionso Combustion Reactions;
o Write the chemical equation for the combustion of hexane.
Writing Chemical Equations
• Empirical Formulaso A reduced version of the ratio of atoms in a
compound.
C10H22 (molecular formula)
C5H11 (empirical formula)
Writing Chemical Equations
• Empirical Formulaso We can calculate an empirical formula if we know the
percent by mass of the elements in a compound.
Percent by Mass = mass of element in compound x 100 total mass of compound
Writing Chemical Equations
• Empirical Formulaso Calculate the percent mass of each element in the
compound C6H12.
o Calculate the emprical formula of this compound.
Writing Chemical Equations
• Empirical Formulaso Calculate the molar mass of the compound if its
molecular weight is 84.18 g/mol.
Writing Chemical Equations
• Avogadro’s Number – The Moleo Amedeo Avogadro (1600’s)
o Developed a way to quantify gas particles.o Calculated that a container that had a volume
of 22.4L would contain 6.02 x 1023 gas particles.
Writing Chemical Equations
• The Moleo Relates the mass of a substance with the
number of representative particles and molar volume.
Writing Chemical Equations
• Mole Conversionso Convert 20.0 grams of NaCl into moles.
o Convert 0.35 moles of carbon tetrabromide into grams.
Writing Chemical Equations
• Mole Conversionso Convert 10.0 L of CO2 into moles
at STP.
o Convert 1.80 moles of ammonia into liters.
Writing Chemical Equations
• Mole Conversionso Convert 5.63 x 1015 atoms of iron into moles.
o Convert 0.0025 moles of magnesium atoms into moles.
Writing Chemical Equations
• Mole Conversionso Convert 1.2 x 1025 molecules of oxygen gas into grams.
o Convert 500.0 Liters of nitrogen dioxide into grams.
Writing Chemical Equations
• Stoichiometric Conversions
Writing Chemical Equations
• Stoichiometric Conversionso Molar Ratios – A conversion factor constructed from the coefficients of a balanced chemical reaction.
O2(g) +2H2(g) 2H2O(g)
Writing Chemical Equations
• Stoichiometric Conversionso What volume of water vapor can be produced if 10.00 grams of oxygen gas reacts with an
excess of hydrogen gas?O2(g) +2H2(g) 2H2O(g)
Writing Chemical Equations
• Stoichiometric Conversionso How many grams of lead(II)iodide can be produced if 5.00 grams of potassium iodide
reacts with an excess of lead(II)nitrate?2KI(aq) + Pb(NO3)2(aq) 2KNO3(aq) + PbI2(s)
Writing Chemical Equations
• Limiting Reactantso 1.00 gram of iron is allowed to react with 1.00 gram of
nitrogen gas to form iron(II)nitride.3Fe(s) + N2(g) Fe3N2(s)
Which is the limiting reagent?
What mass of iron(II)nitride will be produced?
Writing Chemical Equations
• Limiting Reactantso 1.00 gram of iron is allowed to react with 1.00 gram of
nitrogen gas to form iron(II)nitride.3Fe(s) + N2(g) Fe3N2(s)
Which is the reagent in excess?
What mass of the reagent in excess will remain after the reaction has stopped?
Writing Chemical Equations
• Limiting Reactantso Tin and nitric acid will react to form tin(IV)oxide,
nitrogen dioxide, and water. 8.00 grams of nitric acid is added to a 20.0 gram sample of tin.
What volume of nitrogen dioxide will be collected at STP?
Writing Chemical Equations
• Limiting Reactantso Tin and nitric acid will react to form tin(IV)oxide,
nitrogen dioxide, and water. 8.00 grams of nitric acid is added to a 20.0 gram sample of tin.
What mass of the reagent in excess will remain after the reaction has stopped?
Writing Chemical Equations
• Calculating Percent Yieldo The percent yield of a chemical reaction is a measure
of its efficiency.
% yield = Actual Amount Recovered x 100 Theoretic Amount
Writing Chemical Equations
• Calculating Percent Yieldo 100.0 mL of fluorine gas is bubbled through a solution
that contains 4.00 grams of calcium bromide. Calcium fluoride and 1.5 grams of liquid bromine is produced. Calculate the percent yield of this chemical reaction.