1.6 Chemical Equilibria
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What is a closed system?
No chemicals can get in or out during a reaction
What are the features of a dynamic system?
Closed Forwards and backwards reactions are happening at the same time
What are the features of a reaction at equilibrium?
Rate of forwards reaction is equal to backwards reaction Concentration of reactants and products remain the same
What factors effect equilibrium?
Temperature Concentration Pressure (only in gases)
What affect does a catalyst have on equilibrium?
Speed up rate but does not influence equilibrium
What is Le Chateliers principle?
Position of equilibrium will shift to oppose a change
What is the effect of changing the temperature of a reaction?
• Depends on whether it is endo or exothermic • If forward reaction is exothermic it will shift to left • If forward reaction is endothermic it will shift to right
What is the effect of increasingthe pressure/concentration?
Moves the equilibrium to the side with the lowest number of moles
What is the effect of increasing pressure if moles are equal on both sides?
Pressure has no effect
What is the way to obtain the greatest yield from the Haber process?
• High pressure • Low temperature • High Concentration • Remove NH3 as it’s produced
What are the compromised conditions for the Haber process?
• Lower pressure 200 atm • Higher temperature of 450c to maintain a fast enough reaction • Iron catalyst (allows for lower temperature)
What is a Homogenous equilibrium?
• All reactants and products are in the same state
What is a heterogenous equilibrium?
• More than one state is present
What is not included in an equilibrium constant reaction?
• Solids and pure liquids
What is the equilibrium constant?
aA + bB >< cC + dD
What is the equilibrium law equation?
Kc= [C] ^c + [D] ^d ——————— [A]^a + [B] ^b (Concentrations of)
How are units of Kc calculated?
Using the same formula for calculating the values but inputting the concentrations units e.g (moldm^-3 x moldm^-3)
What is the definition of equilibrium constant?
Constant for a particular reaction at a particular temperature in solution (moldm^-3)
When does equilibrium constant change?
ONLY WHEN TEMPERATURE CHANGES
What does a Kc value over 1 mean?
Forward reaction dominates
How do you calculate equilibrium quantities?
Initial moles - Change in moles
Why is (Br or Cl) added to swimming pools when it’s toxic?
Usually a Hydroxide is added which reacts with H+ ions Equilibrium will shift to oppose decrease in H+ ions increasing yield of less toxic stuff Leaves only a small amount of toxic halogen which will kill bacteria but not people