Thermochemistry

I. The Nature of Energy
A. Energy is the capacity to do work or to produce heat. Energy can be converted from one form to another but neither created nor destroyed. Potential energy is energy due to position or composition. Kinetic energy is energy due to motion and is equal to mass times velocity squared.
B. Temperature is a property that reflects the random motions of the particles in a particular substance. Heat involves the transfer of energy between two objects due to a temperature difference. Work is defined as force acting over a distance. A state function is a function that is independent of the path. In other words, a state function depends only on the present state.
C. In a chemical reaction, there is the system which is the part of the universe where the reaction is taking place and the surroundings are everything else. A reaction that is exothermic dumps energy into the surroundings while a reaction that is endothermic takes energy away from the surroundings.
D. The study of energy and its interconversions is called thermodynamics. The internal energy of a system can be defined most precisely as the sum of the kinetic and potential energies of the "particles" in the system. The change in energy of a system is equal to the sum of heat and work.
E. With a gas expanding in a cylinder the work being done by the gas is given by the formula PDV.

II. Enthalpy and Calorimetry
A. At constant pressure, the change in enthalpy DH of the system is equal to the energy flow as heat. In other words, the flow of heat is a measure of the change in enthalpy.
B. The device used experimentally to determine that heat associated with a chemical reaction is called a calorimeter. The heat capacity of a substance, which is a measure of this property is defined as C=heat absorbed/increase in temperature. If the heat capacity is given per gram of substance, it is called the specific heat capacity, and its units are J/g°C.

III. Hess's Law
A. The sum of all the steps in a reaction gives the net, or overall, reaction and the sum of the steps enthalpies equals the enthalpy of the net reaction. If a reaction is reversed the sign of the change in enthalpy also changes. The magnitude of the DH is proportional to the quantities of reactants and products in a reaction.

IV. Standard Enthalpies of Formation
A. The standard enthalpy of formation of a compound is defined as the change in enthalpy that accompanies the formation of one mole of a compound from its elements with all substances in their standard states. The enthalpy change for a given reaction can be calculated by subtracting the enthalpies of formation of the reactants from the enthalpies of formation of the products.