Endothermic and Exothermic

Reactions

Energy and Reactions

Energy is involved in chemical reactions in two ways:

1. to break some (or all) bonds between atoms in the reactants so the atoms can form new bonds or

2. when the atoms or products form new bonds to make new products.

Two Types of Reactions

We classify chemical reactions based on how the energy of the reactants compares to the energy of the products.

Exothermic reactions

If forming new bonds releases more energy than it takes to break the old bonds, the reaction is exothermic.

Exothermic reactions

A good example is the reaction of hydrogen with oxygen.

Once started, exothermic reactions tend to keep going as each reaction releases more energy to fuel neighboring molecules.

Endothermic reactions

If forming new bonds in the products releases less energy than it took to break the original bonds, the reaction is endothermic.

Endothermic reactions

An important endothermic reaction is photosynthesis.

Plants need energy from sunlight to make glucose and oxygen from carbon dioxide and water.

EXOTHERMIC ENDOTHERMIC

Chemical reactions where HEAT…Is transferred to the surroundings…Indicated by a RISE in temperature

Chemical reactions where HEAT…Is transferred from the surroundings …Indicated by a FALL in temperature

Endothermic – energy absorbed melting vaporization sublimation

EXOTHERMIC-Energy lost freezing condensation deposition

Activation Energy

Activation energy is the energy needed to begin a reaction and break chemical bonds in the reactants.

Activation Energy

This is why a flammable material like gasoline does not burn without a spark or flame.

Examples of Endothermic Reactions

Most of the reactions used in industry to produce useful materials require more energy than they produce.

One process that uses endothermic reactions is the refining of ores to produce useful metals.

Examples of Endothermic Reactions

Most of the reactions used in industry to produce useful materials require more energy than they produce.

The reaction taking place inside an instant cold pack is endothermic.

Examples of Endothermic Reactions

When you squeeze the plastic bag the water reacts with the ammonium nitrate crystals, and the reaction dissolves the ionic bonds in the ammonium nitrate.

Examples of Endothermic Reactions

ACTIVITY

Complete graph Matching with Partner.

Very endothermic reaction with a big activation energy

Very exothermic reaction with a small activation energy

.

Moderately endothermic reaction with a moderately high activation energy.

Energy level diagram for an exothermic chemical reaction without showing the activation energy. It could also be seen as quite exothermic with a highly unlikely zero activation energy, but reactions between two ions of opposite charge usually has a very low activation energy.Could usually has a very low activation energy.

Exothermic withoutShowing activationenergy

Moderately exothermic reaction with a moderately high activation energy

en as, probably impossible?).

EndothermicWithout activation Energy being shown

Energy level diagram for an exothermic chemical reaction without showing the activation energy. It could also be seen as quite exothermic with a highly unlikely zero activation energy, but reactions between two ions of opposite charge usually has a very low activation energy. Energy level diagram for an exothermic chemical reaction

without showing the activation energy. It could also be seen as quite zero activation energy, but reactions between two ions of opposite charge usually has a very low activation energy.

Energy isequal. PossibleBut not likely

Create a SONGPOEMDRAWING to explain The difference betweenEndothermic and Exothermic reactions.Pg. 86 in book.

1. Explain the differenceBetween endo and exo Reactions.2. Draw a graph of eachType. Endo and exoLabel each3. Write an equation for each

Words to be usedEndothermicExothermicActivation energyAbsorbedReleased