Topic: Potential Energy Curve

Do Now: p.26

Spontaneous Processes=physical or chemical change that occurs with no outside intervention

• However, some energy may be supplied to get process started = activation energy

Iron rusting4Fe(s) + 3O2(g) 2Fe2O3(s)

H = -1625 kJ

Combustion CH4(g) + 2O2(g) CO2(g) + 2H2O(l) H = -891kJ

Can you think of others?

VIDEO

Activation Energy & Reaction

Activation Energy

• = Energy needed to initiate reaction

• Energy needed to overcome reaction barrier

• difference between where reactants start & top of hill

• Difference between reactants & activated complex

Energy Diagram of a ReactionActivated Complex = intermediate formed during conversion from reactants to productsReactants combine to form an unstable complex

Potential Energy Curve: Endothermic

Products have more P.E. than reactants

Start low, end high

Potential Energy Curve: Exothermic

Products have less P.E. than reactants

Start high, end low

Have to label 6 energies on curve: reactants & products

1. PE reactants2. PE products3. PE activated complex4. Ea forward reaction

5. Ea reverse reaction

6. H

Time

What kind of reaction is represented?

PE reactants

PE activated complex

PE products

Ea forward rxn

Ea reverse rxn

40

30

20

10

Enth

alpy

H of reaction

40

30

20

10

Enth

alpy

Time

What kind of reaction is represented?

PE of reactants

PE of activated complex

P.E. of products

Ea forwardrxn

Ea

reverserxn

40

30

20

10

Enth

alpy

H of reaction

40

30

20

10

Enth

alpy

Catalyst (in the body = enzyme)

• Substance that increases rate of reaction without itself being consumed –does not participate in reaction

• Lowers the activation energy for the reaction

DOES IT AFFECT ΔH?Catalysts do not affect ΔH