AP Chemistry Unit 4

Big Idea:

Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of Electrons

The laws of thermodynamics describe the essential role of energy and explain and predict the direction of changes in matter.

Student Expectations:

Focus Standards

Enduring understanding 3.C: Chemical and physical transformations may be observed in several ways and typically involve a change in energy.

Essential knowledge

• 3.C.2: Net changes in energy for a chemical reaction can be endothermic or exothermic.
• 3.C.3: Electrochemistry shows the interconversion between chemical and electrical energy in galvanic and electrolytic cells.

Enduring understanding 3.B: Chemical reactions can be classified by considering what the reactants are, what the products are, or how they change from one into the other. Classes of chemical reactions include synthesis, decomposition, acid-base, and oxidation-reduction reactions.

• 3.B.3: In oxidation-reduction redox) reactions, there is a net transfer of electrons. The species that loses electrons is oxidized, and the species that gains electrons is reduced.

Enduring understanding 5.A: Two systems with different temperatures that are in thermal contact will exchange energy. The quantity of thermal energy transferred from one system to another is called heat.

Essential knowledge

• 5.A.1: Temperature is a measure of the average kinetic energy of atoms and molecules.
• 5.A.2: The process of kinetic energy transfer at the particulate scale is referred to in this course as heat transfer, and the spontaneous direction of the transfer is always from a hot to a cold body.

Enduring understanding 5.B: Energy is neither created nor destroyed, but only transformed from one form to another.

Essential knowledge

• 5.B.1: Energy is transferred between systems either through heat transfer or through one system doing work on the other system.
• 5.B.2: When two systems are in contact with each other and are otherwise isolated, the energy that comes out of one system is equal to the energy that goes into the other system. The combined energy of the two systems remains fixed. Energy transfer can occur through either heat exchange or work.
• 5.B.3: Chemical systems undergo three main processes that change their energy: heating/ cooling, phase transitions, and chemical reactions.
• 5.B.4: Calorimetry is an experimental technique that is used to determine the heat exchanged/transferred in a chemical system.

Enduring understanding 5.C: Breaking bonds requires energy, and making bonds releases energy.

Essential knowledge

• 5.C.1: Potential energy is associated with a particular geometric arrangement of atoms or ions and the electrostatic interactions between them.
• 5.C.2: The net energy change during a reaction is the sum of the energy required to break the bonds in the reactant molecules and the energy released in forming the bonds of the product molecules. The net change in energy may be positive for endothermic reactions where energy is required, or negative for exothermic reactions where energy is released.

Enduring understanding 5.D: Electrostatic forces exist between molecules as well as between atoms or ions, and breaking the resultant intermolecular interactions requires energy.

Essential knowledge

• 5.D.1: Potential energy is associated with the interaction of molecules; as molecules draw near each other, they experience an attractive force.
• 5.D.2: At the particulate scale, chemical processes can be distinguished from physical processes because chemical bonds can be distinguished from intermolecular interactions.
• 5.D.3: Noncovalent and intermolecular interactions play important roles in many biological and polymer systems.

Enduring understanding 5.E: Chemical or physical processes are driven by a decrease in enthalpy or an increase in entropy, or both.

Essential knowledge

• 5.E.1: Entropy is a measure of the dispersal of matter and energy.
• 5.E.2: Some physical or chemical processes involve both a decrease in the internal energy of the components (ΔH° < 0) under consideration and an increase in the entropy of those components (ΔS° > 0). These processes are necessarily “thermodynamically favored” (ΔG° < 0).
• 5.E.3: If a chemical or physical process is not driven by both entropy and enthalpy changes, then the Gibbs free energy change can be used to determine whether the process is thermodynamically favored.
• 5.E.4: External sources of energy can be used to drive change in cases where the Gibbs free energy change is positive.
• 5.E.5: A thermodynamically favored process may not occur due to kinetic constraints (kinetic vs. thermodynamic control).

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 3 The student can engage in scientific questioning to extend thinking or to guide investigations within the context of the AP course.

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.

Science Practice 7 The student is able to connect and relate knowledge across various scales, concepts and representations in and across domains.

Student Learning Targets:

• Design and/or interpret the results of an experiment in which calorimetry is used to determine the change in enthalpy of a chemical process (heating/cooling, phase transition, or chemical reaction) at constant pressure. [LO 5.7, SP 4.2, SP 5.1, SP 6.4]
• Generate explanations or make predictions about the transfer of thermal energy between systems based on this transfer being due to a kinetic energy transfer between systems arising from molecular collisions. [LO 5.3, SP 7.1]
• Use conservation of energy to relate the magnitudes of the energy changes occurring in two or more interacting systems, including identification of the systems, the type (heat versus work), or the direction of energy flow. [LO 5.4, SP 1.4, SP 2.2, connects to 5.B.1, 5.B.2]
• Use conservation of energy to relate the magnitudes of the energy changes when two nonreacting substances are mixed or brought into contact with one another. [LO 5.5, SP 2.2, connects to 5.B.1, 5.B.2]
• Draw qualitative and quantitative connections between the reaction enthalpy and the energies involved in the breaking and formation of chemical bonds. [LO 5.8, SP 2.3, SP 7.1, SP 7.2]
• Use calculations or estimations to relate energy changes associated with heating/ cooling a substance to the heat capacity, relate energy changes associated with a phase transition to the enthalpy of fusion/ vaporization, relate energy changes associated with a chemical reaction to the enthalpy of the reaction, and relate energy changes to PΔV work. [LO 5.6, SP 2.2, SP 2.3]
• Use representations and models to predict the sign and relative magnitude of the entropy change associated with chemical or physical processes. [LO 5.12, SP 1.4]
• Predict whether or not a physical or chemical process is thermodynamically favored by determination of (either quantitatively or qualitatively) the signs of both ΔH° and ΔS°, and calculation or estimation of ΔG° when needed. [LO 5.13, SP 2.2, SP 2.3, SP 6.4, connects to 5.E.3]
• Determine whether a chemical or physical process is thermodynamically favorable by calculating the change in standard Gibbs free energy. [LO 5.14, SP 2.2, connects to 5.E.2]
• Explain how the application of external energy sources or the coupling of favorable with unfavorable reactions can be used to cause processes that are not thermodynamically favorable to become favorable. [LO 5.15, SP 6.2]
• Explain why a thermodynamically favored chemical reaction may not produce large amounts of product (based on consideration of both initial conditions and kinetic effects), or why a thermodynamically unfavored chemical reaction can produce large amounts of product for certain sets of initial conditions. [LO 5.18, SP 1.3, SP 7.2, connects to 6.D.1]
• Interpret observations regarding macroscopic energy changes associated with a reaction or process to generate a relevant symbolic and/or graphical representation of the energy changes. [LO 3.11, SP 1.5, SP 4.4]
• Analyze the enthalpic and entropic changes associated with the dissolution of a salt, using particulate level interactions and representations. [LO 6.24, SP 1.4, SP 7.1, connects to 5.E]
• Express the equilibrium constant in terms of ΔG° and RT, and use this relationship to estimate the magnitude of K and, consequently, the thermodynamic favorability of the process. [LO 6.25, SP 2.3]
• Identify redox reactions, and justify the identification in terms of electron transfer. [LO 3.8, SP 6.1]
• Identify redox reactions, and justify the identification in terms of electron transfer. [LO 3.8, SP 6.1] Make qualitative or quantitative predictions about galvanic or electrolytic reactions based on half-cell reactions and potentials and/or Faraday’s laws. [LO 3.12, SP 2.2, SP 2.3, SP 6.4]
• Design and/or interpret the results of an experiment involving a redox titration. [LO 3.9, SP 4.2, SP 5.1]
• Analyze data regarding galvanic or electrolytic cells to identify properties of the underlying redox reactions. [LO 3.13, SP 5.1]
• Make qualitative or quantitative predictions about galvanic or electrolytic reactions based on half-cell reactions and potentials and/or Faraday’s laws. [LO 3.12, SP 2.2, SP 2.3, SP 6.4]

Essential Questions:

• When an auto mechanic informs you that your car battery is “dead,” what does that mean at the molecular level?
• If we say a reaction “takes place,” what factors make that happen?
• If you have metal fillings in your teeth, why does biting on aluminum foil cause so much pain?
• Why do saltwater fishermen place Zn plates on their boats’ engines?

Extra Information:

Adopted Textbook:

District Grading Policy

Texas Gateway Online Resource Center