← Chemistry syllabus

United StatesChemistry

Unit 9: Applications of Thermodynamics

11 dot points across 11 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do we calculate the standard entropy change of a reaction from absolute entropies?

Topic 9.2 Absolute Entropy and Entropy Change: use standard molar entropies to calculate the standard entropy change of a reaction as the sum for products minus the sum for reactants.
A focused answer to AP Chemistry Topic 9.2, covering absolute (standard molar) entropy, why it is positive for all substances, and calculating the standard entropy change of a reaction as products minus reactants, with full worked examples.
9 min answer →

How is the standard cell potential calculated, and how does it relate to the free energy change of a cell reaction?

Topic 9.9 Cell Potential and Free Energy: calculate the standard cell potential from standard reduction potentials, and relate it to the free energy change with delta G standard equals minus n F E standard.
A focused answer to AP Chemistry Topic 9.9, covering the standard cell potential from standard reduction potentials, the sign of the cell potential and spontaneity, and the relationship delta G standard equals minus n F E standard, with full worked examples.
11 min answer →

How does the cell potential change when the concentrations are not standard, and what happens as a cell discharges?

Topic 9.10 Cell Potential Under Nonstandard Conditions: predict how the cell potential changes with concentration using the Nernst relationship qualitatively, and explain why a cell potential falls to zero at equilibrium.
A focused answer to AP Chemistry Topic 9.10, covering how the cell potential changes with concentration, the qualitative use of the Nernst relationship and the reaction quotient Q, concentration cells, and why a cell reaches zero potential at equilibrium, with full worked examples.
10 min answer →

How can a thermodynamically unfavorable reaction be driven by coupling it to a favorable one?

Topic 9.7 Coupled Reactions: explain how an unfavorable reaction can be driven by coupling it to a favorable reaction so that the combined free energy change is negative.
A focused answer to AP Chemistry Topic 9.7, covering how coupling an unfavorable reaction to a more favorable one gives a net negative free energy change, the role of a shared intermediate, and biological and industrial examples, with full worked examples.
9 min answer →

How do we calculate the amount of substance produced at an electrode from the current and time using Faraday's law?

Topic 9.11 Electrolysis and Faraday's Law: use the current, time and the moles of electrons to calculate the mass or amount of substance produced at an electrode during electrolysis.
A focused answer to AP Chemistry Topic 9.11, covering electrolysis, the relationship between charge, current and time, Faraday's constant, and calculating the mass or moles of substance deposited or produced at an electrode, with full worked examples.
11 min answer →

How are the standard free energy change and the equilibrium constant related?

Topic 9.5 Free Energy and Equilibrium: relate the standard free energy change to the equilibrium constant using delta G standard equals minus RT ln K, and use delta G equals delta G standard plus RT ln Q for non-standard conditions.
A focused answer to AP Chemistry Topic 9.5, covering the relationship between the standard free energy change and the equilibrium constant, delta G standard equals minus RT ln K, the non-standard delta G equation, and how the sign of delta G standard relates to the size of K, with full worked examples.
11 min answer →

How do enthalpy, entropy and free energy together explain the thermodynamics of dissolving a salt?

Topic 9.6 Free Energy of Dissolution: analyze the dissolution of a salt using delta G equals delta H minus T delta S, and relate the sign of delta G to whether and how much the salt dissolves.
A focused answer to AP Chemistry Topic 9.6, covering the thermodynamics of dissolution, how the enthalpy and entropy of solution combine into the free energy, and how the sign of delta G relates to solubility and Ksp, with full worked examples.
10 min answer →

How do galvanic and electrolytic cells use redox reactions to convert between chemical and electrical energy?

Topic 9.8 Galvanic (Voltaic) and Electrolytic Cells: describe the structure and operation of galvanic and electrolytic cells, identifying the anode, cathode, electron flow and the direction of energy conversion.
A focused answer to AP Chemistry Topic 9.8, covering galvanic (voltaic) and electrolytic cells, the anode and cathode, electron and ion flow, the salt bridge, and the direction of energy conversion in each cell type, with full worked examples.
11 min answer →

How does the Gibbs free energy combine enthalpy and entropy to determine whether a process is thermodynamically favorable?

Topic 9.3 Gibbs Free Energy and Thermodynamic Favorability: use the equation delta G equals delta H minus T delta S to determine thermodynamic favourability and the temperature dependence of spontaneity.
A focused answer to AP Chemistry Topic 9.3, covering the Gibbs free energy equation, how the signs of enthalpy and entropy determine favourability, the temperature dependence of spontaneity, and the four sign cases, with full worked examples.
11 min answer →

What is entropy, and how do we predict the sign of the entropy change for a process?

Topic 9.1 Introduction to Entropy: describe entropy as a measure of the dispersal of energy and matter, and predict the sign of the entropy change for physical and chemical processes.
A focused answer to AP Chemistry Topic 9.1, covering entropy as the dispersal of energy and matter, the factors that increase entropy, and predicting the sign of the entropy change for phase changes, dissolving and gas-mole changes, with full worked examples.
9 min answer →

Why can a thermodynamically favorable reaction still fail to proceed at a noticeable rate?

Topic 9.4 Thermodynamic and Kinetic Control: distinguish thermodynamic favourability (sign of delta G) from kinetic feasibility (rate), and explain why a favorable reaction may be slow.
A focused answer to AP Chemistry Topic 9.4, covering the distinction between thermodynamic favourability and kinetic feasibility, why a favorable reaction can be slow due to a high activation energy, and the role of catalysts, with full worked examples.
9 min answer →