Summary Chem 103 Module 3 Notes.

Thermodynamics is the study of the relationship between heat and other forms of energy, particularly mechanical work. Thermochemistry is the part of thermodynamics that deals with the quantity of heat given off or absorbed during a chemical reaction. The quantity of heat given off or absorbed during a physical change or temperature change can also be studied, and we will refer to this process as calorimetry. In order to adequately discuss thermochemistry, we need to define some common terms. System - the object (or substance) being studied Open system - a system that permits the transfer of mass and energy with the surroundings Closed system - a system that permits the transfer of energy but not mass with the surroundings Isolated system - a system that does not permit the transfer of energy or mass with the surroundings Surroundings - the rest of the universe interacting with the system Energy - the potential or capacity to move matter: the ability to do work (unit is J = joule) Work - the amount of energy transferred by a force acting through a distance Kinetic energy - the energy possessed by an object by virtue of its motion (unit is J = joule) Potential energy - the energy possessed by an object by virtue of its position (unit is J = joule) Heat (q) - the thermal energy transferred between system and surroundings due to a difference in temperature between them (unit is J = joule) Enthalpy - the total energy of a system Heat of reaction - (ΔH) the amount of heat (q) gained or lost during a chemical reaction Exothermic - a reaction with a - ΔH Endothermic - a reaction with a + ΔH You must be able to use the terms above to describe a thermochemical system. Calorimetry The energy change that accompanies a physical, temperature, or chemical change is determined by carrying out the process in a device known as a calorimeter. The calorimeter is able to measure the amount of heat absorbed or evolved as a process takes place. A Styrofoam coffee cup calorimeter can be used to measure an energy change that takes place at constant pressure. An enclosed bomb calorimeter is used to measure an energy change that takes place at constant volume with a change in pressure. We will use the term calorimetry to refer particularly to measuring energy changes that accompany temperature and physical change (state change or phase change) processes. Temperature change calorimetry measures the thermal energy change occurring as a system at higher temperature transfers kinetic energy to a system at lower temperature, which is reflected by a change in temperature for the overall system. This is demonstrated below by adding a 15.6-gram piece of aluminum (heated to 100oC) to a 45.6 gram sample of water at 26.7oC in a coffee cup calorimeter. The final temperature