# Entropy and Free Energy 19.3. After reading Section 19.3, you should know: What entropy and free energy are How to determine whether the entrophy is increasing.

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Entropy and Free Energy 19.3

After reading Section 19.3, you should know: What entropy and free energy are How to determine whether the entrophy is increasing or decreasing based on a chemical equation How to determine whether a reaction will be spontaneous or not.

Free Energy – the amount of energy available to do work Energy that can be obtained by a reaction only if the reaction actually (not theoretically) occurs

Spontaneous reactions - reactions that occur naturally release free energy favor the formation of products H 2 CO 3 --> H 2 O + CO 2 *** this reactant will produce more than 99% of the products Spontaneous or Nonspontaneous?

Nonspontaneous reactions - reactions that do not tend to occur absorb free energy do not favor the formation of products not efficient (use a lot of energy) H 2 O + CO 2 --> H 2 CO 3 *** these reactants will produce less than 1% of the products Spontaneous or Nonspontaneous?

Entropy – a quantitative measure of the disorder of a system Reactions want to be in disorder

Entropy increases when… a change in state occurs (solid --> liquid --> gas) a substance is divided into parts

Entropy increases when… if the number of product molecules is greater than the number of reactant molecules H 2 O (g) H 2(g) + O 2(g) when the temp increases

How are Enthalpy, Entropy and Free Energy all related??? Enthalpy (heat energy) and Entropy (disorder) determine whether a reaction is spontaneous or not Spontaneous if reaction produced small amounts of energy with high disorder Nonspontaneous if reaction produced large amounts of energy with low disorder

If energy is high and disorder is high OR If energy is low and disorder is low THEN Spontaneity will depend on the strength of each

Helpful References Table 19.1 (pg 554) Figure 19.20 (pg 555)

After reading Section 19.3, you should know: What entropy and free energy are How to determine whether the entrophy is increasing or decreasing based on a chemical equation How to determine whether a reaction will be spontaneous or not.

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