Thermochemistry

Thermochemistry is the study of the energy changes that accompany physical or chemical changes in matter

Energy is the ability to do work. It is measured in joules (J)

It can be classified as either…

1. Potential energy: the energy of a body or system due to its position or composition

2. Kinetic energy: the energy of.an object due to its motion

Thermal Energy

The total quantity of potential and kinetic energy of a substance is called thermal energy. In general, thermal energy depends on how fast the atoms/ions/molecules of the substance are moving.

Heat: the transfer of thermal energy from hot object to cold object

Temperature is a measure of the average kinetic energy of entities in a substance

If a substance absorbs heat from the surroundings, the particles move faster

If a substance releases heat to the surroundings, the particles slow down

Analyzing Energy Conversions in Chemical Reactions

It is useful to divide the universe into two parts

1. Chemical System: a group of reactants and products being studied

2. Surroundings: all of the matter that is not part of the system

Types of Chemical Systems

1. Open System: matter and energy are free to enter and leave a system

2. Closed System: energy can enter and leave, but matter cannot

The total energy in a chemical system and its surroundings must be the same before and after a chemical reaction

Energy Changes in Chemical Reactions

Atoms bond with other atoms in order to form a more stable structure. Breaking the bonds requires energy

If more energy is released from the formation of new bonds in the products than is required to break the bonds in the reactants, the chemical system will release energy to the surroundings. This is called an exothermic reaction.

A reaction that absorbs thermal energy from its surroundings is called an endothermic reaction.