Chapter 3The Driving Forces

Exothermic & Endothermic Entropy

•All changes whether physical or chemical involve a change in energy.

•Energy can be released during the change (exothermic).

•Energy may be absorbed during the change (endothermic).

•The amount of energy that is released or absorbed in measured in joules or calories.

Energy Change and Bond Breakage/Formation

Energy Change and Bond Breakage/Formation

• Bonds are energy.• Each different type of bond has an amount of energy

associated with it.

Energy Change and Bond Breakage/Formation

• Bonds are energy.• Each different type of bond has an amount of energy

associated with it.• When we break a bond the process requires energy (it is

endothermic).• When we form a bond the process releases energy (it is

exothermic).• The net energy change determines whether the reaction

is endothermic or exothermic.

Energy Change and Bond Breakage/Formation

2H─H + :O ═ O: → 2

Energy Change and Bond Breakage/Formation

•We can often determine whether energy is being released or absorbed by a reaction by determining if any temperature change occurs.

Temperature Change

• Exothermic reactions “often” feel hot.

• Endothermic reactions “often” feel cold.

See the page in your notes titled “The Driving Forces”

EXOTHERMIC ENDOTHERMIC

release energy absorb energy products are lower in energy than the reactants products are higher in energy than the reactants generally cause surroundings to heat up generally cause the surroundings to cool down nature favors these reactions nature opposes these reactions Bond formation Bond breakage

Spontaneous vs. Nonspontaneous

• A spontaneous process is a process that occurs without outside intervention.

• No external forces are required to keep the process going, although external forces may be required to get the process started.

Activation Energy

• The activation energy is the amount of energy that must be added to a reaction for it to occur.

• Both exothermic and endothermic reactions require activation energy.

Spontaneous vs. Non-spontaneous

• A non-spontaneous process will not occur naturally.

The Driving Forces

• All reactions (changes) in nature occur because of the interplay of two driving forces:

(1) The drive toward lower energy.

(2) The drive toward increased randomness.

Entropy

• Entropy is the amount of randomness (lack of order) in a system.

Some call it entropy. I call it heaven

Entropy

• Entropy is how “chaotic”, (disordered), a system is.

Some call it entropy. I call it heaven

Increase in Entropy

Increase in Entropy

• Production of liquid or gas from a solid.

Increase in Entropy

• Production of gas from a liquid.

Entropy

Increase in Entropy

• Formation of a mixture.

Increase in Entropy

• More particles are created.

The mixing of the white solids which I did earlier was spontaneous. Why?

Release Energy

Increase Entropy