Kc

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  • Created by: ava.scott
  • Created on: 10-02-15 10:56

equilibrium law

The equilibrium law tells us the relative proportions of reactants and products at equilibrium.

a dynamic equilibrium:

  • Rate of forward reaction is equal to the backwards reaction.
  • The concentrations of products and reactants remains the same.
  • it is a closed system.

EQUILIBRIUM MUST BE A HOMOGENOUS SOLUTION.

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Kc values

A kc value of 1 indicates the equilibrium is positioned halfway between reactants and products.

if Kc is smaller than 1 (<1) the reactants are favoured, and the left side of the equation is predominant at equilibrium .

if Kc is larger than 1 (>1) the products are favoured, and the right side of the equation is predominant at equilibrium.

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Temperature increase and Kc

Increase in temperature, shifts the position of equilibrium to endothermic reaction.

- if the forward reaction is exothermic, this will increase the backwards reaction, causing a decrease in products and therefore a decrease in Kc.

- if the forward reaction is endothermic, the forward reaction will be favoured, increasing products and therefore Kc.

KC FOLLOWS PRODUCTS.

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Temperature decrease and kc

Decrease in temperature shifts the position of equilibrium to the exothermic reaction.

- if the forward reaction is exothermic, this will increase the forwards reaction, causing a increase in products and therefore a increase in Kc.

- if the forward reaction is endothermic, the backwards reaction will be favoured, decreasing products and therefore Kc.

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Kc and concentration

 Concentration

If the concentrations are changed the system is no longer in equilibrium, so kc cannot be measured.

The equilibrium will shift to change the new reactants to products.

This will reestablish Kc, as concentration of both reactants and products go up.

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kc and pressure

pressure

If pressure is doubled, the concentrations of both reactants and products will eventually be doubled, so kc is not affected.

The equilibrium shifts to maintain Kc by favouring the side with more gaseous moles.

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kc and catalyst

catalyst

catalyst speeds up rate of reaction, but not the position of equilibrium.

no effect on kc

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Using initial moles and equilbrium moles

S-some: START MOLES

C-cunning: CHANGE MOLES TO

E-elves: EQUILIBRIUM MOLES

M-murdered: MOLES>CONCENTRATION (divide by volume in dm3)

K-ken: KC-(subsitute concs into expression)

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Le chateliers principle

A dynamic equilibrium will shift to counteract any chnages that occur within a closed system.

Temperature

  • Increase- endothermic reaction will be favoured
  • Decrease- exothermic reaction will be favoured

Pressure

  • Increase- side will less gaseous moles will be favoured
  • Decreases- side with more gaseous moles will be favoured

Concentration

  • equilbrium will shift to comvert those molecules into other type.
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