• Unit 6: Thermochemistry and Thermodynamics

    In this unit, we study thermochemistry, which deals with the temperature- and heat-related aspects of chemistry, and thermodynamics, which focuses on the overall energies associated with chemical reactions. Thermodynamics will lead us to the Gibbs free energy equation, which tells us whether a chemical reaction is spontaneous (or will occur without external help).

    Completing this unit should take you approximately 10 hours.

    • 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

      • 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.

      • 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 the enthalpy of a system.

      • 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 1 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 2 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.

      • 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.

      • Hess' Law and Reaction Enthalpy Change Page

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

      • Heats of Reaction and Hess' Law URL

        This virtual lab will demonstrate Hess' Law using three reactions: the solubility of NaOH in water, the solubility of 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.

      • 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

      • 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.

      • The First Law of Thermodynamics and Internal Energy Page

        Watch this lecture, which covers exothermic and endothermic reactions.

      • The Availability of Energy URL

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

      • 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.

      • Gibbs 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 while a reaction may be predicted to be spontaneous, its reaction rate may be very slow.

      • Gibbs Free Energy and Spontaneity 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.