• ### Unit 6: Thermochemistry and Thermodynamics

In this unit, we study thermodynamics and thermochemistry. Thermodynamics is the study of heat transfer. Thermochemistry is specifically the study of heat transfer in chemical reactions. We were introduced to thermodynamics in Unit 5 when we learned about the energy associated with phase changes. Thermodynamics and thermochemistry allow us to predict whether a reaction will produce heat, such as the burning of a candlewick, or if a reaction will require heat to proceed, such as the reaction that occurs inside a disposable cold pack. In this unit we also learn about Gibbs Free Energy, which tells us whether a reaction is spontaneous, meaning the reaction will occur without external "help".

Completing this unit should take you approximately 6 hours.

• ### 6.1: Energy

Before we begin our study of thermodynamics and thermochemistry, we need some definitions.

Thermodynamics incorporates many everyday words, such as energy, heat, work, system, and surroundings, which have precise meanings in this scientific context. In thermodynamics, the system refers to whatever you are interested in learning about. For example, the system could be a chemical reaction, or a substance undergoing a phase change. The surroundings refer to everything the system comes into contact with. For example, if you are doing a chemical reaction in a beaker, the system is the reaction and the surroundings are the beaker and air directly surrounding the beaker.

There are two overall types of energy: kinetic and potential. Kinetic energy is the energy of motion. Any object in motion has kinetic energy. Potential energy refers to stored energy that can be due to an object's position, or the energy stored in chemical bonds. Heat refers to the disordered flow of energy between a system and its surroundings when there is a temperature difference. Work refers to the ordered flow of energy between a system and its surroundings when there is not a temperature difference.

• ### 6.2: Thermodynamics

Thermodynamics is the general study of heat and energy transfer. It is governed by the three laws we will examine in this section. Some chemists call the first law of thermodynamics 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.