Reversible Reactions Flashcards
Enthalpy change and endothermic VS exothermic reactions
If delta H is positive, it is an endothermic reaction (heat is absorbed)
If delta H is negative, it is exothermic (heat is released)
Examples of irreversible reactions
Combustion of coal
Reaction of acid with limestone
Examples of reversible reactions
Thermal decomposition
Haber process
Contact process (sulfur dioxide to make sulfur trioxide)
Esterification
Dynamic equilibrium
Dynamic equilibrium refers to a reversible process at equilibrium in which rates of forward and backward reaction are equal
What is Le Chatelier’s principle?
Le Chatelier’s principle states that if a system is subjected to a change which disturbs the equilibrium, the system responds in such a way to counteract the effect of the change
Le Chatelier’s principle concentration
According to Le Chatelier’s principle, equilibrium will shift in a direction that will partially consume a reactant or product that is added, or partially replace a reactant or product that is removed
Le Chatelier’s principle pressure and volume
According to Le Chatelier’s principle, if the pressure of a gaseous mixture is increased the system will adjust itself to reduced the pressure by shifting to the direction which will decrease the number of gaseous molecules and hence the pressure exerted by the gas
Le Chatelier’s principle temperature
According to Le Chatelier’s principle, if the temperature of an equilibrium mixture increases, the system will adjust itself to reduce the temperature by shifting the equilibrium towards the endothermic direction to absorb some of the heat energy
Presence of a catalyst
Catalysts in rates the rates of both the forward and backward direction by the same extent so equilibrium can be established faster
However, it does not have any effect on equilibrium position
Conditions used in the Haber process
Temperature: 450 degrees
Pressure: 250 atm
Catalyst: finely divided iron
Explanation for temperature used in Haber process
By Le Chatelier’s principle, given that reaction is exothermic lowering the temperature shifts the equilibrium to the right and in rates the yield of ammonia
However, reaction is extremely slow at low temperature. Therefore, moderately high temperature of 450 degrees must be used to increase the rate of reaction
Explanation for pressure used in Haber process
By Le Chatelier’s principle, increasing the pressure shifts the equilibrium to the right and increase the rate of reaction thus increasing the equilibrium yield of ammonia
However, very high pressure is expensive as the cost and maintenance of equipments used in plants becomes higher
