CHEM101: General Chemistry I

Unit 6: Thermochemistry and Thermodynamics

• Upon successful completion of this unit, you will be able to:

  • define temperature;
  • define heat and state its units;
  • define and perform enthalpy change, enthalpy of reaction, enthalpy of combustion, and enthalpy of formation calculations;
  • define entropy;
  • describe the driving force of a chemical reaction and relate it to Gibbs free energy;
  • define Hess' law and state its functions; and
  • use Hess' law to solve thermodynamic problems.

• 6.1: Energy

  • Stephen Lower's "General Chemistry Virtual Textbook: Energy, Heat, and Work" URL

    Read this page. Pay close attention to how the system and surroundings are defined; this will determine the direction of energy flow in thermodynamic systems.
    

  • Stephen Lower's "General Chemistry Virtual Textbook: Molecules as Energy Carriers and Converters" URL

    Read this page. Make sure you can follow the concept map at the bottom of the page, which relates potential and kinetic chemical energy to enthalpy of a system.
    

  • Khan Academy: "Enthalpy" and "Heat of Formation" Page

    Watch these videos. The enthalpy of a system is the energy contained in its chemical bonds plus any pressure-volume work the system can do.
    

  • Virtual Lab: "Camping Problem I" URL

    In this virtual lab, you will measure the enthalpy of a reaction. To see the instructions, click the name of the problem ("Camping 1") on the virtual lab screen.
    

  • Virtual Lab: "Camping Problem II" URL

    In this virtual lab, you will determine change in the enthalpy of a reaction as the concentration of reactants are varied. To see the instructions, click the name of the problem ("Camping 2") on the virtual lab screen.
    

  • Stephen Lower's "General Chemistry Virtual Textbook: Thermochemistry and Calorimetry" URL

    Read this page. Calorimetry is used to measure the change in enthalpy of reactions in a laboratory setting. Since enthalpy is a state function, Hess' law is applied to calculate the change in enthalpy from literature values.
    

  • Khan Academy: "Hess's Law and Reaction Enthalpy Change" and "Hess's Law Example" Page

    Watch these videos to reinforce your understanding of Hess' Law.
    

  • Virtual Lab: "Heats of Reaction and Hess' Law" URL

    This virtual lab will demonstrate Hess' Law using three reactions: the solubility NaOH in water, the solubility NaOH in HCl and the reaction of a solution of HCl and a solution of NaOH. To see the instructions, click the name of the problem ("Heats of Reaction") on the virtual lab screen.
    

  • Stephen Lower's "General Chemistry Virtual Textbook: Some Applications of Enthalpy and the First Law" URL

    Read this page. Using bond energy to calculate the enthalpy of reaction is not particularly accurate because energies are affected by each molecule's unique surroundings, such as intermolecular forces. For this reason, energies are only an average across many different reactions.
    

• 6.2: Thermodynamics

  • Stephen Lower's "General Chemistry Virtual Textbook: The First Law of Thermodynamics" URL

    Read this page. The first law of thermodynamics is sometimes referred to as the law of conservation of energy. It states that energy can be neither created nor destroyed, but it may change form. For example, imagine a campfire: the energy is stored in chemical bonds in the wood, and is released as light and heat.
    

  • Khan Academy: "First Law of Thermodynamics/Internal Energy" Page

    Watch this lecture, which covers exothermic and endothermic reactions.
    

  • Stephen Lower's "General Chemistry Virtual Textbook: The Second Law of Thermodynamics: The Availability of Energy" URL

    Read this page. The second law of thermodynamics deals with heat transfer and also explains why a perpetual motion machine can never exist.
    

  • Stephen Lower's "General Chemistry Virtual Textbook: What is Entropy?" URL

    Read this page, which gives a detailed description of entropy and how it relates to the system and surroundings. The third law of thermodynamics deals with a theoretical absolute zero state, which is a physical impossibility.
    

  • Stephen Lower's "General Chemistry Virtual Textbook: The Gibbs Function (Gibbs Energy): Free Energy" URL

    Read this page. The Gibbs free energy equation predicts whether a reaction will happen spontaneously or not. Gibbs free energy applies to reactions of every magnitude, from water freezing to industrial chemical processes. It is important to note that whereas a reaction may be predicted to be spontaneous, the reaction rate may be very slow however.
    

  • Khan Academy: "Gibbs Free Energy and Spontaneity" and "Gibbs Free Energy Example" Page

    Watch these videos. If the computed change in Gibbs free energy is negative for a chemical reaction, then the reaction is spontaneous.
    

• Unit 6 Assessment

  • Unit 6 Assessment Quiz

    Take this assessment to see how well you understood this unit.

    • This assessment does not count towards your grade. It is just for practice!
    • You will see the correct answers when you submit your answers. Use this to help you study for the final exam!
    • You can take this assessment as many times as you want, whenever you want.