Download Name - Holland Public Schools

Outline: “Let’s Get Energized”
Hour ____ Date _______ Name ________________________
I. Energy is stored in Chemical Bonds
 Energy – The ability to do work
A. During Chemical Reactions, there is always a change in Properties & Energy
Breaking bonds takes energy  Making Bonds releases energy
Example:
1. Potential Energy (PE)
Stored Energy
2. Kinetic Energy (KE)
Energy of Motion
B. Energy Changes
1. If PE ___ , then KE ___.
2. If PE ___ , then KE ___.
II. Chemical Reactions & Energy Changes
A. Gaining Energy?
1. Endothermic Reaction
a. Endo – “Into”
Therm – “Heat”
b. Heat Energy “into” a chemical rxn
 ∆ HE – (Delta HE) Change in Heat Energy
c. ∆ HE negative; Products are COLD!
B. Losing Energy?
1. Exothermic Reaction
a. Exo – “Exit” Therm – “Heat”
b. Heat Energy “exiting” a chemical rxn
c. ∆ HE positive; Products are HOT!
III. Let’s Get It Started!
A. Activation Energy (AE)
1. Energy needed to get a reaction started
2. Every reaction has some AE
Energy - Endothermic and Exothermic.
A chemical reaction always has a change in energy.
In a reaction going from reactants to products, either
1) Heat is given out - called Exothermic
or
2) Heat is taken in - called Endothermic.
The large majority of reactions are exothermic, they give heat out.
Some physical processes are associated with a change in energy.
Melting and boiling are endothermic,
Freezing and condensing are exothermic.
Breaking bonds (overcoming the force of attraction) requires energy,
you have to put heat in - it is endothermic.
This is why melting and boiling are endothermic.
Making bonds gives out energy - it is exothermic.
This is why freezing and condensing are exothermic.
In a chemical reaction
you need to put energy in to break bonds in the reactants,
you get energy out when new bonds are formed to make the products.
If you get out more energy than you have to put in,
then overall the reaction is exothermic.
This is what normally occurs.
If you have to put in more energy than you get out,
then the reaction is endothermic,
but except in rare circumstances, the reaction doesn't happen.
Going from reactants to the top of the curve,
you are going up the energy scale.
Energy (heat) is being put in to break bonds in the reactants.
At the top of the curve, the bonds in the reactants have been broken.
The amount of energy put in to break these bonds
is called the activation energy.
The activation energy
is the minimum amount of energy needed for the reaction to occur.
A catalyst may work by lowering the activation energy for a reaction.
Going from the top of the curve to the products,
you are going down the energy scale.
Energy (heat) is given out as bonds form in the products.
The reactants are higher up the energy scale than are the products.
The amount of energy (heat) you need to put in (the activation energy)
is less than the amount of energy (heat) you get out.
This is a typical exothermic reaction.
The difference in energy levels between the reactants and the products
is given the symbol H (pronounced 'delta H').
This is the amount of heat given out (or taken in) during the reaction.
For an exothermic reaction, H is negative.
For an endothermic reaction, H is positive.