section 3.3 stoichiometry and chemical reactions
DESCRIPTION
Section 3.3 Stoichiometry and Chemical Reactions. In this section: a. Chemical reactions and equations b. Balancing equations c. Reaction stoichiometry. Chemical reactions and equations Reactants Products. CH 3 CHCH 2 + HCl. CH 3 CHClCH 3. - PowerPoint PPT PresentationTRANSCRIPT
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Section 3.3Stoichiometry and Chemical Reactions
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In this section:
a. Chemical reactions and equationsb. Balancing equationsc. Reaction stoichiometry
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Chemical reactions and equations
Reactants Products
CH3CHCH2 + HCl CH3CHClCH3
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Chemical equation: before and after
Mechanism: how you get there
Step 1.
Step 2.
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The most important thing:
It’s the same atoms
Reactants Products
CH3CHCH2 + HCl CH3CHClCH3
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The Law of Conservation of MatterIt’s the same atoms
Stoichiometric Coefficients:
CH3CHCH2 + HCl CH3CHClCH3
C2H2 + 2 H2 CH3CH3
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Balancing Chemical Equations
Goal: same number of atoms of each element on both sides
Rule: you can change stoichiometry coefficients, not the molecular formulas
CH4 + O2 CO2 + H2O
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A bit harder
C4H10 + O2 CO2 + H2O
Another Example:
Mg + O2 MgO
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Big misconception: stoichiometric coefficients are NOT how much reacts/forms
CH4 + 2 O2 CO2 + 2 H2O
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Balancing Equation = mol to mol conversion factor
CH4 + 2 O2 CO2 + 2 H2O
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Amounts tables: If 0.46 mol O2 react, how much CO2 and H2O are formed, and how much CH4 reacts?
CH4 + 2 O2 CO2 + 2 H2Ochange:
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Real experiments use mass, not moles.
gram gram conversions
Path:
grams A moles A moles B grams B
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CH4 + 2 O2 CO2 + 2 H2O
25.0 g of O2 react. What mass of CH4 reacts and what masses of CO2 and H2O are formed?
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CH4 + 2 O2 CO2 + 2 H2O
25.0 g of O2 react. What mass of CH4 reacts and what masses of CO2 and H2O are formed?
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Sections 3.4 and 3.5Limiting Reactants, Percent Yield and
Chemical Analysis
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In these sections:
a. Identifying limiting reactantsb. Calculating theoretical yieldc. Calculating percent yieldd. Chemical analysis
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The Idea of Limiting Reactants
If you have 200 tires and 75 steering wheels, how many cars can you make?
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Identifying Limiting ReactantsIf you have 200 tires and 75 steering wheels, how many cars can you make?
4 tires + 1 steering wheel 1 car
Mole Ration Method:
Maximum Product Method:
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Using Amounts Tables: after determining limiting reactant
Initial amounts: Fe2O3: 100 g = 0.626 molC: 50.0 g = 4.16 mol
2 Fe2O3 + 3 C 4 Fe + 3 CO2
initial
change
final
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Percent Yield
mass of product actually obtainedPercent yield = 100%theoretical maximum mass that could have been obtained
experimental yieldPercent yield = 100%theoretical yield
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actual experimental yield% Yield = 100%theoretical calculated yield
Alum Lab Calculations:Let’s say you start with 0.985 g Al and actually make 14.8 g KAl(SO4)212 H2O product. What is the percent yield?
Molar masses: Al = 26.98 g/mol; KAl(SO4)212 H2O = 474.37 g/mol
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Chemical Analysis: Using stoichiometry to determining how much of one thing is in anotherA sample of soil is analyzed for the element iodine. A 2.68-g sample is treated so all the iodine containing compounds dissolve and the iodine is converted to iodide ion. The solution is treated with dissolved Pb2+ ion, and the following reaction occurs:
Pb2+(aq) + 2 I-(aq) PbI2(s)If 0.339 g of PbI2 are obtained, what was the percent iodine in the original sample?
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Chemical Analysis: Determining FormulasCHO Analyzer
burn: 0.588 g sample collect: 0.240 g H2O 0.882 g CO2