chapter 6 - equilibria Flashcards
Define dynamic equilibrium
1) Equilibrium in a closed system [container] nothing can enter or leave
2) The rate of forward and backward reactions are equal
3) The concentration of reactants and products does not change
Define homogenous equilibrium
Has all reactants in the same state. Both the reversible systems above all homogenous e.g. [gaseous].
Define heterogeneous equilibrium
All of the reactants are in different states
Define a forward reaction
There is more product than reactant and the equilibrium shifts to the right hand side. The forward reaction is said to be favoured
Define backward reactions
There is more reactant than product the equilibrium will shift to the left hand side and the backward reaction is said to be favoured
Le Chateliers principal
A system at equilibrium will oppose any change imposed upon it
CO2 + 3H2 = CH3OH + H2O
delta H = -49 KJmol-1
effect of concentration on equilibrium
if the concentration of carbon dioxide was increased how would this affect the yield of methanol?
Increasing the concentration of carbon dioxide causes the equilibrium to shift to oppose the change. The equilibrium will shift to the right and the forward reaction is favoured to remove and decrease the concentration of carbon dioxide. The position of the equilibrium will shift to the right to produce a higher yield of methanol.
CO2 + 3H2 = CH3OH + H2O
delta H = -49 KJmol-1
Effect of temperature on equilibrium
If the temperature decreased how will this affect the yield of methanol.
if the temperature decreased the equilibrium will shift to increase the temperature and oppose the change. This will shift the equilibrium to the right in the more exothermic direction so the yield of methanol increases and the forward reaction is favoured.
CO2 + 3H2 = CH3OH + H2O
delta H = -49 KJmol-1
Effect of pressure on equilibrium
if the pressure in the system is increased how will this affect the yield of methanol
The system will try to oppose the change and decrease the pressure. equilibrium will shift to the right and the forward reaction is favoured this increases the yield of methanol as the equilibrium moves to the side with fewer moles of gas.
CO2 + 3H2 = CH3OH + H2O
delta H = -49 KJmol-1
The effect of equilibrium when a catalyst is added
what would happen to the yield of methanol if a catalyst is added to the reaction
there would be no affect on the position of the equilibrium as a catalyst will speed up the rate of reaction (the rate at which equilibrium is achieved) it does not affect the position of the equilibrium because it speeds up the rate of the forward and backward reactions by the same amount.
overall the effect of temperature on equilibrium
If the temperature in the equilibrium is increased the equilibrium will shift and moves in the endothermic direction to try to reduce the temperature by absorbing heat.
if the temperature in the equilibrium is decreased the equilibrium will shift and move in the exothermic direction to try to increase the temperature by giving out heat.
overall the effect of pressure on equilibrium
Increasing the pressure will cause the equilibrium to shift to the side with fewer moles of gas, To oppose the change and try to decrease the temperature.
Decreasing the pressure will cause the equilibrium to shift to the side with more moles of gas, To oppose the change and try to increase the temperature.
If the number of gas molecules is the same on both sides of the equation then changing the pressure will have no affect on the position of the equilibrium.
High-pressure leads to high energy costs. To have equipment that can withstand high-pressure this will cost a lot of money.
Overall the effect of a catalyst on equilibrium
A catalyst has no
affect on the position of the equilibrium but will speed up the rate of reaction.
Catalysts however speed up the rate, allowing a lower temperature to be used (hence lower the energy costs) but have no affect on the position of equilibrium.
define carbon neutral
An activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere.
Effects on equilibrium in the harbour process and compromises
N2 + 3H2 = 2NH3
delta H = -92.4 KJmol-1
theoretical conditions Low temperatures (highest yield) high-pressure (highest yield)
actual conditions
Low temperatures take a long time to produce ammonia and high pressure is costly. therefore compromise conditions are used and the normal yield for ammonia is around 15 to 20%.
