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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 rusting 4Fe(s) + 3O 2 (g)  2Fe 2 O 3 (s)  H = -1625 kJ.

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Spontaneous processes
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 rusting

4Fe(s) + 3O2(g)  2Fe2O3(s)

H = -1625 kJ

CombustionCH4(g) + 2O2(g)  CO2(g)+ 2H2O(l)

H = -891kJ





Activation energy
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 reaction

Activated Complex = intermediate

formed during conversion from reactants to products

Reactants combine to form an unstable complex

Energy Diagram of a Reaction


Potential energy curve endothermic
Potential Energy Curve: Endothermic

Products have more P.E. than reactants

Start low, end high


Potential energy curve exothermic
Potential Energy Curve: Exothermic

Products have less P.E. than reactants

Start high, end low


Have to label 6 energies on curve reactants products
Have to label 6 energies on curve: reactants & products

  • PE reactants

  • PE products

  • PE activated complex

  • Ea forward reaction

  • Ea reverse reaction

  • H


PE

reactants

Time

What kind of reaction is represented?

40

Ea

reverse rxn

Ea

forward rxn

30

Enthalpy 

20

PE activated complex

PE products

10


40

30

Enthalpy 

H of reaction

20

10


Ea

forward

rxn

Ea

reverse

rxn

40

30

Enthalpy 

PE of activated complex

20

PE of reactants

10

P.E. of products

Time

What kind of reaction is represented?


40

30

Enthalpy 

20

H of reaction

10


Catalyst in the body enzyme
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


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