← Chemistry syllabus

United StatesChemistry

Unit 6: Thermodynamics

9 dot points across 9 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How can the enthalpy of a reaction be estimated from the energies of the bonds broken and formed?

Topic 6.7 Bond Enthalpies: estimate the enthalpy change of a reaction from average bond enthalpies, using the rule that breaking bonds absorbs energy and forming bonds releases it.
A focused answer to AP Chemistry Topic 6.7, covering average bond enthalpies, the principle that breaking bonds is endothermic and forming bonds is exothermic, and estimating the enthalpy of reaction as bonds broken minus bonds formed, with full worked examples.
10 min answer →

What distinguishes an endothermic process from an exothermic one at the level of energy and bonds?

Topic 6.1 Endothermic and Exothermic Processes: classify a process as endothermic or exothermic from the direction of energy flow, the sign of the enthalpy change and the bonds broken and formed.
A focused answer to AP Chemistry Topic 6.1, covering the distinction between endothermic and exothermic processes, the sign of the enthalpy change, the direction of energy flow between system and surroundings, and the bond-breaking and bond-forming picture, with full worked examples.
9 min answer →

How does an energy diagram represent the relative potential energies of reactants and products and the enthalpy of a reaction?

Topic 6.2 Energy Diagrams: draw and interpret an energy diagram showing the relative enthalpies of reactants and products and the enthalpy change of the reaction.
A focused answer to AP Chemistry Topic 6.2, covering how an energy diagram represents the relative potential energies of reactants and products, the sign of the enthalpy change for endothermic and exothermic reactions, and how to read the diagram, with full worked examples.
9 min answer →

Why does temperature stay constant during a phase change, and how is the energy of a phase change calculated?

Topic 6.5 Energy of Phase Changes: explain why temperature is constant during a phase change, interpret a heating curve, and calculate the energy of a phase change from the enthalpy of fusion or vaporisation.
A focused answer to AP Chemistry Topic 6.5, covering heating curves, why temperature is constant during melting and boiling, the enthalpy of fusion and vaporisation, and calculating the energy of a phase change, with full worked examples.
10 min answer →

What is a standard enthalpy of formation, and how is it used to calculate the enthalpy of a reaction?

Topic 6.8 Enthalpy of Formation: use standard enthalpies of formation to calculate the enthalpy of a reaction as the sum for products minus the sum for reactants.
A focused answer to AP Chemistry Topic 6.8, covering the standard enthalpy of formation, the zero value for elements in their standard states, and calculating the enthalpy of a reaction as products minus reactants, with full worked examples.
10 min answer →

How do we calculate the heat exchanged using specific heat capacity, and how does calorimetry measure it?

Topic 6.4 Heat Capacity and Calorimetry: use the equation q equals mc delta T with specific heat capacity, and use calorimetry data to determine the heat of a process.
A focused answer to AP Chemistry Topic 6.4, covering specific heat capacity, the equation q equals mc delta T, calorimetry, and how to determine the heat and enthalpy of a process from temperature data, with full worked examples.
11 min answer →

How does heat flow between objects at different temperatures, and what does thermal equilibrium mean?

Topic 6.3 Heat Transfer and Thermal Equilibrium: explain heat transfer as the flow of energy from a hotter object to a cooler one until thermal equilibrium is reached, relating it to the kinetic energy of particles.
A focused answer to AP Chemistry Topic 6.3, covering heat transfer from hot to cold objects, the particle-level meaning of temperature and kinetic energy, thermal equilibrium, and the conservation of energy in heat exchange, with full worked examples.
9 min answer →

How does Hess's law let us combine known reactions to find the enthalpy of a reaction we cannot measure directly?

Topic 6.9 Hess's Law: use Hess's law to determine the enthalpy of a reaction by combining the enthalpies of a series of reactions that add to the target, reversing and scaling as needed.
A focused answer to AP Chemistry Topic 6.9, covering Hess's law, the additivity of enthalpy as a state function, and how to reverse, scale and add reactions to find an unknown enthalpy of reaction, with full worked examples.
11 min answer →

What is the enthalpy of reaction, and how is it used in stoichiometric (thermochemical) calculations?

Topic 6.6 Introduction to Enthalpy of Reaction: interpret the enthalpy of reaction as a state function and use thermochemical equations to relate the heat of a reaction to the amount of substance reacted.
A focused answer to AP Chemistry Topic 6.6, covering the enthalpy of reaction as a state function, thermochemical equations, the meaning of the sign of delta H, and how to scale the heat of a reaction with the amount reacted, with full worked examples.
10 min answer →