Deciding Order of Reactions

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Deciding Order of Reactions

• St. Albans High School
• Honors Chemistry II
• Carol Kuhlman
• October 29, 1999

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Summary of Kinetics Reactions

• Zero Order Reactions
• Rate k
• Graph of A versus t is a straight line
• slope -k
• Half life t 1/2 A/ 2k

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First Order

• Rate kA
• Graph of lnA verses t is a straight line
• slope -k
• Half life t 1/2 0.693/k

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Second Order

• Rate k A2
• Graph of 1/A verses t is a straight line.
• Slope k
• Half life t 1/2 1/k A0

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One way to decide what the reaction order is
would be to examine the data and look at the 3
different graphs.

• A vs. t
• ln A vs. t
• 1/A vs. t

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The graph that gives you the best resolution for
a straight line will be the reaction order.
Determining the rate law this way is known as the
integrated rate law.
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Practice with this data
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Heres Another Way to Decide Order of Reactions

• Zero Order m 0, rate is independent of
  concentration. Doubling the concentration of the
  reactant does not affect the rate.

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First Order m 1, rate is directly
proportional to the concentration of the reactant.

• Doubling the concentration of the reactant
  doubles the rate.

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Second Order m 2, rate is proportional to the
square of the concentration of the reactant.

• Doubling the the concentration increases the rate
  by a factor of 4.
• The above 3 methods are known as the differential
  rate law.

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Lets Practice!!!!
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The previous data was from the reaction 2X
Y ? 3Z

• What is the proper rate expression?

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REMEMBER!!!!

• Rate Change in Concentration
• Change in Time
• Rate k An Bm Cp

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The type of data determines whether we use the
differential rate law or the integrated rate law.
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WV IGOs

• C.8 3,4,5,6,7,8,9,10
• C.10
• C.11
• C.13
• C.17

• C.18
• C.21
• C.44
• C.73
• C.74

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• C.8 Demonstrates science processes within a
  problem solving setting.
• C.10 Identify, analyze, and infer using patterns
  and relationships in data.
• C.11 Use SI (metric) measurements.
• C.13 Use the tools of science safely, accurately,
  and appropriately.
• C.17 Engage in activities, investigations, and
  hands on activities to develop conceptual
  understanding.

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• C.18 Properly and safely manipulate equipment,
  materials, chemicals, and models.
• C.21 Review of foundational chemical concepts
  including chemical symbols representing kinetic
  molecular theory.
• C.44 Experimentally determine the factors that
  influence the rate of reaction.

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• C.73 Access, gather, store, retrieve, and
  organize data using hardware and software
  designed for these purposes.
• C.74 Collect, analyze and display data using
  computers and other electronic technology.

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Bibliography

• Chemistry, 4th Edition, Zumdahl, Steven S.,
  Houghton Mifflin Company, Boston, MA., 1997
• Workbook for General Chemistry, Shakhashiri and
  Schreiner, The University of Wisconsin-Madison,
  Stipes Publishing, Champaign, IL, 1996

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• Advanced Placement Chemistry Preparation Guide,
  Thorpe, Gary S., Cliffs Notes, Lincoln, Nebraska,
  1994.
• Chemistry With the CBL, Vernier Software,
  Portland, Oregon, 1997.