Chemical Reactions
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Transcript of Chemical Reactions
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 3Slide 1 of 24
PHILIP DUTTONUNIVERSITY OF WINDSOR
DEPARTMENT OF CHEMISTRY AND BIOCHEMISTRY
TENTH EDITION
GENERAL CHEMISTRYPrinciples and Modern Applications
PETRUCCI HERRING MADURA BISSONNETTE
Chemical Reactions 4
Chemical Compounds
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 3Slide 2 of 24
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 3 of 24
4-1 Chemical Reactions and Chemical Equations
As reactants are converted to products we observe:Color change
Precipitate formation
Gas evolution
Heat absorption or evolution
Chemical evidence may be necessary.
Precipitation of silver chromate
Figure 4-1
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 3Slide 4 of 24
Evidence of a chemical reaction
Figure 4-2
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 3Slide 5 of 24
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 6 of 24
Chemical Reactions
Nitrogen monoxide + oxygen → nitrogen dioxide
Step 1: Write the reaction using chemical symbols.
NO + O2 → NO2
Step 2: Balance the chemical equation.
2 1 2
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 7 of 24
Molecular Representation
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 8 of 24
Balancing Equations
Never introduce extraneous atoms to balance.
NO + O2 → NO2 + O
Never change a formula for the purpose of balancing an equation.
NO + O2 → NO3
An equation can be balanced only by adjusting the coefficients of formulas.
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 9 of 24
Balancing Equation Strategy
Balance elements that occur in only one compound on each side first.
Balance free elements last.
Balance unchanged polyatomics (or other groups of atoms) as groups.
Fractional coefficients are acceptable and can be cleared at the end by multiplication.
States of Matter
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 3Slide 10 of 24
(g) gas (l) liquid (s) solid
Thus, the equation for combustion of triethylene glycol can be written as
2 C6H14O4(l) + 15 O2(g) 12 CO2(g) + 14 H2O(l)
Another commonly used symbol for reactants or products dissolved in water is
(aq) aqueous solution
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 11 of 24
4-2 Chemical Equations and Stoichiometry
Stoichiometry includes all the quantitative relationships involving:
atomic and formula masses
chemical formulas.
chemical equations
• Mole ratio or stoichiometric factor is a central conversion factor.
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 3Slide 12 of 24
KEEP IN MIND
that it is important to include units and to work from a balanced chemical equation when solving stoichiometry problems.
A generalized stoichiometry diagram
Figure 4-3
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 3Slide 13 of 24
The reaction of 2 Al(s) 6 HCl(aq) 2 AlCl3(aq) 3 H2(g)Figure 4-4
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Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 15 of 24
4-3 Chemical Reactions in Solution
Close contact between atoms, ions and molecules necessary for a reaction to occur.
Solvent
We will usually use aqueous (aq) solution.
Solute
A material dissolved by the solvent.
Molarity
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 16 of 24
Molarity (M) = Volume of solution (L) Amount of solute (mol solute)
If 0.440 mol of urea is dissolved in enough water to make 1.000 L of solution the concentration is:
curea = 1.000 L
0.440 mol urea = 0.440 M CO(NH2)2
C = V n
Solution Dilution
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 17 of 24
Figure 4-6
Visualizing the dilution of a solution
Mi × Vi = ni
Mi Vi Mf Vf
= nf = Mf × Vf
M = n
V
Mi × ViMf = Vf
= Mi
Vi
Vf
Preparation of 0.250 M K2Cr2O7 —Example 4-9 illustratedFigure 4-5
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 18 of 24
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 19 of 24
4-4 Determining Limiting Reagent
The reactant that is completely consumed determines the quantities of the products formed.
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 20 of 24
Theoretical yield is the expected yield from a reactant.Actual yield is the amount of product actually produced.
Percent yield = 100%Actual yield
Theoretical Yield
4-5 Other Practical Matters in Reaction Stoichiometry
Theoretical, Actual and Percent Yield
Theoretical, Actual and Percent Yield
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 21 of 24
actual yield = theoretical yield
quantitative
Side reactions reduce the percent yield.
By-products are formed by side reactions.
Consecutive Reactions, Simultaneous Reactions and Overall Reactions
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 22 of 24
Multistep synthesis is often unavoidable.
Reactions carried out in sequence are called consecutive reactions.
When substances react independently and at the same time the reaction is a simultaneous reaction.
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 23 of 24
Overall Reactions and Intermediates
The Overall Reaction is a chemical equation that expresses all the reactions occurring in a single overall equation.
An intermediate is a substance produced in one step and consumed in another during a multistep synthesis.
Copyright © 2011 Pearson Canada Inc.General Chemistry: Chapter 4Slide 24 of 24
End of Chapter Questions
Initial problem solving is linear and often based on memorizing solutions for particular situations.
Answer
a
bc