Equilibria FINAL -_-

Slide 1

• Reversible Reactions
• Reversible reactions are where reactions can go in both forward and backward directions.
• Forward reaction
• -Initially reactants are used up quickly but then slow as their concentration drops.
• Backward Reaction
• --Initially reactants are reformed slowly, but then speed up as the concentration of products increases.
• [Arrow] At this point, the rate of the forward reaction equals the rate of the backwards reaction. We call this a DYNAMIC EQUILIBRIUM.
• The concentration of each substance remains constant.
• -->Only occurs in closed systems
• -->DON'T GET THIS CONFUSED: NOT SAME AS
• "THE AMOUNT OF REACTANT AND PRODUCT IS THE SAME".
• 

Slide 2

• Le Chatelier's Principle
• If a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will move to counteract the change.
• If the change in the condition results results in equilibrium shifting to the left we make more reactants
• 3H2 (g) + N2 (g) -> <- 2NH3 (g)
• If the change in the condition results in equilibrium shifting to the right, we make more products.
• 3H2 (g) + N2 (g) -> <- 2NH3 (g)

Slide 3

• Le Chatelier's Principle-- Changing Concentration
• LCP: If a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will move to counteract the change.
• If we increase the concentration of a reactant or product the equilibrium will shift to try to reduce the concentration. (The opposite will happen if concentration is decreased).
• If we increase the concentration of H2, equilibrium will shift to the right to use it up and reduce the concentration, and more NH3 will be produced.
• 3H2 (g) + N2 (g) -> <- 2NH3 (g)
• If we increase the concentration of NH3, equilibrium will shift to the left to use it up and reduce the concentration. More H2 and N2 will be produced.
• 3H2 (g) + N2 (g) -> <- 2NH3 (g)
• This only works in HOMOGENEOUS EQUILIBRIA (reactants and products in the same state).

Slide 4

• LCP- Changing Pressure
• LCP: If a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will move to counteract the change.
• If we increase the pressure, the equilibrium will shift to try to reduce the pressure. (The opposite will happen if pressure is decreased)
• If we increase the pressure, equilibrium will shift to the side with the fewest number of gas particles, reducing the pressure. More NH3 will be produced.
• 3H2 (g) + N2 (g) -> <- 2NH3 (g)
• If we decrease the pressure, equilibrium will shift to the side with the most number of gas particles, increasing the pressure. More N2 and H2 will be produced.
• 3H2 (g) + N2 (g) -> <- 2NH3 (g)
• This only works in HOMOGENEOUS EQUILIBRIA (reactants and products in the same state).

Slide 5

• Le chatelier's principle- changing temperature.
• LCP: If a reaction at equilibrium is subjected to a change in pressure, temperature, or concentration, the position of equilibrium will move to counteract the change.
• If we increase the temperature the equilibrium will shift to try to reduce the temperature. (The opposite will happen if the temperature is decreased).
• Forward reaction is exothermic. Delta H is negative.
• If we increase the temperature, the equilibrium will shift in the endothermic direction, reducing the temperature. More N2 and H2 will be produced.
• 3H2 (g) + N2 (g) -> <- 2NH3 (g) ΔH= -46.2 KJmol-1.
• If we decrease the temperature, the equilibrium will shift in the exothermic direction, increasing the temperature. More NH3 will be produced.
• 3H2 (g) + N2 (g) -> <- 2NH3 (g) ΔH= -46.2 KJmol-1
• This only works in HOMOGENEOUS EQUILIBRIA (reactants and products in the same states).

Slide 6

• LCP- Catalysts
• LCP: If a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will move to counteract the change.
• Catalysts have NO EFFECT on the position of equilibrium.
• A catalyst will speed up the rate of the forward and backward reaction equally.
• A catalyst will speed up the rate at which equilibrium is reached, but has no effect on the yield.

Slide 7

• LCP- Making ethanol.
• C2H4 (g) + H2O -> <- C2H5OH (g) ΔH= -46KJmol-1
• Pressure: 60atm
• Temp: 300 degrees Celcius
• Catalyst: Phosphoric Acid (H3PO4)
• Temp: Forward reaction is exothermic, so decreasing the temperature will mean equilibrium shifts to the right, producing more ethanol.
• However, a lower temperature means lower rate of reaction. 300 Degrees celcius is a compromise between yield and rate..
• Pressure: High pressure means equilibrium shifts right, producing more ethanol. Less moles of gas on the right so equilibrium shifts right to reduce pressure. High pressure increases rate too.
• However, high pressure environments are expensive due to thicker, more robust vessels and pipes needed. There is a compromise between yield/speed and cost.

Slide 8

• Kc- The equilibrium constant
• Kc can be worked out form the molar concentration in a reaction.
• The molar values in front of each species are powers in the Kc expression.
• 2A+ B -> <- 2C + D
• Square brackets means concentration of...
• Kc=[C]^2 [D]/ [A]^2 [B]
• Reactants Products