# Energy

Energy is defined in science as the ability to do work. It is a scalar physical quantity. Although energy is conserved, there are many different types of energy, such as kinetic energy, potential energy, light, sound, and nuclear energy. One form of energy may be converted into another without violating a law of thermodynamics. When energy is "lost", it means the energy can't be recaptured for use. This usually occurs when heat is produced.

(1) Kinetic energy is the energy associated with motion; the faster an object moves, the more kinetic energy it has. There is an equation which governs this

K.E. = (1/2) mv2

Where m means mass and v is velocity. This equation means that the general units on kinetic energy are:

(mass) (distance)2 (time)¯2

(2) Potential energy is energy that is stored by virtue of position. There are several different types of storage, of which these four are examples.

#### (a) Gravitational :

this is the most familiar. A rock poised to roll down a hill has potential energy. A ball thrown into the air gains more and more potential energy as it rises. The higher in the gravity field you go, the more potential energy you gain. Generally speaking, chemistry does not concern itself with the potential energy from gravity.

#### (b) Electrical :

in certain materials, you can remove electrons from one area and send them to another. The area losing the electrons becomes more and more positive and the area gaining them becomes negative. The greater and greater the charge difference, the more energy is stored within the system. An example of this is a storm cloud about to "hurl" a lightning strike Earthwards.

#### (c) Chemical :

this is slightly more complex. Certain chemicals have bonds which require little energy to break. This energy must be put into the bond to break it. However, during the course of the chemical reaction, new bonds form which give off MORE energy than that which was put in. Commonly, these reactive compounds are said to "store" energy, but the truth is that the energy released came from a process of first putting in and then getting back more than you put in.

#### (d) Extensive and Intensive Property :

An extensive property is a property that changes when the size of the sample changes. Examples are mass, volume, length, and total charge. An intensive property doesn't change when you take away some of the sample. Examples are temperature, color, hardness, melting point, boiling point, pressure, molecular weight, and density. Because intensive properties are sometimes characteristic of a particular material, they can be helpful as clues in identifying unknown substances.