Energy

Definition

Energy is the ability to do work Work is done on an object whenever a

force (push or pull) moves an object through a distance

Work = Force x Distance

Forms of Energy

Mechanical energy –any energy possessed by macroscopic (visible) objects

Two kinds of mechanical energy

Kinetic Energy

Potential Energy

Potential Energy

Stored energy that is available to do work at a later time

Kinetic Energy

Energy of motion

Unit of Energy

Joule (J) Unit used to be the calorie (cal) 1 cal = 4.19 J How many joules is 1500 calories? How many calories is 36 J?

Conservation of Energy

Whatever changes occur in energy from one type to another, the total amount of energy remains constant

Energy cannot be created or destroyed

Equivalence of Mass and Energy Einstein found that matter and energy

are related Whenever there is a decrease in energy

in a system, there is an increase in mass

Whenever mass increases, energy decreases

New Conservation Law

Old conservation of matter and energy laws were combined

Law of Conservation of Mass and Energy – the total of mass and energy will remain constant in any reaction

                               

Energy in Reactions

In every change, there is a change in energy

Energy change usually more noticeable in chemical changes

Exothermic

If reactants have more chemical energy than the products, then energy must be lost in reaction

This release in heat energy causes the substances to become hot

Chemical reactions that release heat are called EXOTHERMIC

Endothermic Reactions

If products have more chemical energy than reactants, energy must be absorbed

The absorption of heat causes substances to feel cold

This is called an ENDOTHERMIC reaction

Activation Energy

Even though some reactions are exothermic it may still require a little energy to start it off

This starting energy is called ACTIVATION ENERGY