Collision Theory• In a chemical reaction, bonds are broken and new bonds are formed.• Molecules react by colliding with each other.

molecules must collide with the correct orientation and with enough energy to cause bond breakage and formation.

The minimum energy needed for a reaction to take place upon proper collision of reactants = activation energy

The high point on the diagram is the transition state.

The species present at the transition state is called the activated complex.

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• the average rate decreases as the reaction proceeds.

• because as the reaction goes forward, there are fewer collisions between reactant molecules.

C4H9Cl(aq) + H2O(l) C4H9OH(aq) + HCl(aq)

Average rate =

Rate of reaction “how fast” a reactant is used up or a product forms.Increases as the conc. of the reactants increases. More reactants more collisions.

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Higher Temperature increases rate• Increases the number of collisions because reacting molecules move faster.• Collisions are more energetic, providing more colliding molecules with the energy

of activation.

Maxwell–Boltzmann Distributions

• Temperature is defined as a measure of the average kinetic energy of the molecules in a sample.

• At any temperature there is a wide distribution of kinetic energies.

• As the temperature increases, the curve flattens and broadens.• Thus at higher temperatures, a larger population of molecules has higher

energy.4

A catalyst • Speeds up the rate of a reaction.• Lowers the energy of activation. • Is not used up during the reaction.

• Catalysts change the mechanism by which the process occurs.

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One way a catalyst can speed up a reaction is by holding the reactants together and helping bonds to break.

NxOy

CxHy

CO

The metals include platinum, rhodium, and palladium. No more than 4-9 grams of these precious metals are used in a single converter.

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•A reversible reaction can occur in either direction.

CO(g) + H2O(g) CO2(g) + H2(g)

The forward reaction proceeds to the right.

The reverse reaction proceeds to the left.

•The system is at equilibrium when the rate of the forward reaction equals the rate of the reverse reaction.

:. There is no net change in concentration of reactants and products

All chemical reactions are in principle reversible.

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With respect to concentration

With respect to rate

Equilibrium Constant

𝑎𝑡 𝑒𝑞𝑢𝑖𝑙𝑖𝑏𝑟𝑖𝑢𝑚 [𝑅 ]𝑎𝑛𝑑 [𝑃 ]𝑎𝑟𝑒𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡[𝑃 ][𝑅 ]

=𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡=𝐾𝑐 [P] & [R] stand for molar equilibrium concentration

a A + b B c C + d D

The equilibrium constant expression, Kc, gives the molar concentrations of the reactants and products at equilibrium raised to a power based on the coefficients of the balanced equation:

Kc=[CO2]2

[CO]2 [O2]

2CO(g) + O2(g) 2CO2(g)

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R P

The equilibrium constant (K) and reaction quotient (Q).

The equilibrium constant, K, for a reaction has a particular numerical value when reactants and products are at equilibrium. When these are not at equilibrium, however, it is convenient to calculate the reaction quotient, Q.

The expression for Q appears to be just like that of K, but it uses concentrations at any point in the reaction and not necessarily Eq. conc:

a A + b B c C + d D

QTherefore: if Q = K the system is at equilibriumQ<K not at Eq. and RP in order to reach Eq.Q>K not at Eq. and RP in order to reach Eq.

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Heterogeneous Equilibrium

The Kc expression is written in terms of reactants and products whose concentration can change during a chemical reaction. Therefore, it includes only gases and aqueous solutes.

2NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(g)

Kc = [CO2][H2O]

CO2(g) + H2O(l) HCO3-(aq) + H+

(aq)

Kc = [HCO3-][H+]

[CO2]

“concentration” of pure solids and pure liquids is constant and do not appear in the K expression.

Equilibrium with a Large Kc

Equilibrium with a Small Kc

N2(g) + 3Cl2(g) 2NCl3(g)

Kc = [NCl3]2 = 3.2 x 1011

[N2][Cl2]3

a large Kc favors the products

When K 1

[products]

[reactants]

The numerator is larger.

equilibrium lies to the right and favors the products.

N2(g) + O2(g) 2NO(g)

Kc = [NO]2 = 2.3 x 10-9

[N2][O2]

When K 1,

[products]

[reactants] The denominator is larger.

equilibrium lies to the left and favors the reactants.

a small Kc favors the reactants

The magnitude of Kc shows the extent of reaction:

12

= 6.9 × 105 at 230 ˚C

= the reciprocal of the original

1 = 1.5 × 10−6

6.9 × 105

If you reverse the equation, invert the equilibrium constant.

A + 2B 3C

3C A + 2B

K forward = [C]3 [A][B]2

K reverse = [A][B]2 [C]3

= 1__ K forward

For a system at equilibrium:

Example: