AP Chemistry Unit 2

Big Idea:

Student Expectations:

Priority Standards

Big Idea 4: Rates of chemical reactions are determined by details of the molecular collisions.

Focus Standards

Enduring understanding 4.A: Reaction rates that depend on temperature and other environmental factors are determined by measuring changes in concentrations of reactants or products over time.

Essential knowledge

• 4.A.1: The rate of a reaction is influenced by the concentration or pressure of reactants, the phase of the reactants and products, and environmental factors such as temperature and solvent.
• 4.A.2: The rate law shows how the rate depends on reactant concentrations.
• 4.A.3: The magnitude and temperature dependence of the rate of reaction is contained quantitatively in the rate constant.

Enduring understanding 4.B: Elementary reactions are mediated by collisions between molecules. Only collisions having sufficient energy and proper relative orientation of reactants lead to products.

Essential knowledge

• 4.B.1: Elementary reactions can be unimolecular or involve collisions between two or more molecules.
• 4.B.2: Not all collisions are successful. To get over the activation energy barrier, the colliding species need sufficient energy. Also, the orientations of the reactant molecules during the collision must allow for the rearrangement of reactant bonds to form product bonds.
• 4.B.3: A successful collision can be viewed as following a reaction path with an associated energy profile.

Enduring understanding 4.C: Many reactions proceed via a series of elementary reactions.

Essential knowledge

• 4.C.1: The mechanism of a multistep reaction consists of a series of elementary reactions that add up to the overall reaction.
• 4.C.2: In many reactions, the rate is set by the slowest elementary reaction, or rate-limiting step.
• 4.C.3: Reaction intermediates, which are formed during the reaction but not present in the overall reaction, play an important role in multistep reactions.

Enduring understanding 4.D: Reaction rates may be increased by the presence of a catalyst.

Essential knowledge

• 4.D.1: Catalysts function by lowering the activation energy of an elementary step in a reaction mechanism, and by providing a new and faster reaction mechanism.
• 4.D.2: Important classes in catalysis include acid-base catalysis, surface catalysis, and enzyme catalysis.

Ongoing Standards

Science Practice 1 The student can use representations and models to communicate scientific phenomena and solve scientific problems.

Science Practice 2 The student can use mathematics appropriately.

Science Practice 4 The student can plan and implement data collection strategies in relation to a particular scientific question. (Note: Data can be collected from many different sources, e.g., investigations, scientific observations, the findings of others, historic reconstruction and/or archived data.)

Science Practice 5 The student can perform data analysis and evaluation of evidence.

Science Practice 6 The student can work with scientific explanations and theories.

Student Learning Targets:

• Design and/or interpret the results of an experiment regarding the factors (i.e., temperature, concentration, surface area) that may influence the rate of a reaction. [LO 4.1, SP 4.2, SP 5.1]
• Analyze concentration vs. time data to determine the rate law for a zeroth-, first-, or second-order reaction. [LO 4.2, SP 5.1, SP 6.4, connects to 4.A.3]
• Connect the half-life of a reaction to the rate constant of a first-order reaction and justify the use of this relation in terms of the reaction being a first-order reaction. [LO 4.3, SP 2.1, SP 2.2]
• Connect the rate law for an elementary reaction to the frequency and success of molecular collisions, including connecting the frequency and success to the order and rate constant, respectively. [LO 4.4, SP 7.1, connects to 4.A.3, 4.B.2]
• Analyze concentration vs. time data to determine the rate law for a zeroth-, first-, and second-order reaction. [LO 4.2, SP 5.1, SP 6.4, connects to 4.A.3]
• Explain the difference between collisions that convert reactants to products and those that do not in terms of energy distributions and molecular orientation. [LO 4.5, SP 6.2]
• Use representations of the energy profile for an elementary reaction (from the reactants, through the transition state, to the products) to make qualitative predictions regarding the relative temperature dependence of the reaction rate. [LO 4.6, SP 1.4, SP 6.4]
• Evaluate alternative explanations, as expressed by reaction mechanisms, to determine which are consistent with data regarding the overall rate of a reaction, and data that can be used to infer the presence of a reaction intermediate. [LO 4.7, SP 6.5, connects to 4.C.1, 4.C.2, 4.C.3]
• Evaluate alternative explanations, as expressed by reaction mechanisms, to determine which are consistent with data regarding the overall rate of a reaction, and data that can be used to infer the presence of a reaction intermediate. [LO 4.7, SP 6.5, connects to 4.C.1, 4.C.2, 4.C.3]
• Translate among reaction energy profile representations, particulate representations, and symbolic representations (chemical equations) of a chemical reaction occurring in the presence and absence of a catalyst. [LO 4.8, SP 1.5]
• Explain changes in reaction rates arising from the use of acid-base catalysts, surface catalysts, or enzyme catalysts, including selecting appropriate mechanisms with or without the catalyst present. [LO 4.9, SP 6.2, SP 7.2]

Essential Questions:

• The stoichiometry and the kinetics of a reaction are determined from laboratory investigations. How is a mechanism determined?
• When two different collisions occur between two particles, why does only one result in the formation of a product?
• A chemical engineer needs to remove hydrogen peroxide from a solution. What would be the advantages and disadvantages of using a heterogeneous catalyst over a homogeneous catalyst?

Extra Information:

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