The equilibrium principle
Every chemical reaction is in principle reversible. Once products form, the reverse reaction occurs.
Consider the reaction
N2(g) + 3H2(g)
2NH3(g)
As the graphic at the right shows,
As the diagram below shows, if a mixture at equilibrium is allowed to stand, no further change in composition occurs.
For any chemical reaction there are an infinite number of equilibrium compositions. This depends on which components of the system were mixed at the outset and how much of each was used. At equilibrium for reactions described as
The equilibrium state of a reaction at a particular temperature is characterised by a number known as the equilibrium constant (K) that is independent of how the equilibrium system was prepared.
N2(g) + 3H2(g)
2NH3(g)As the graphic at the right shows,
the rate of the forward reaction decreases with time.
the rate of the reverse reaction increases with time.
When these rates are equal, the system is said to be at equilibrium.
the rate of the reverse reaction increases with time.
When these rates are equal, the system is said to be at equilibrium.
As the diagram below shows, if a mixture at equilibrium is allowed to stand, no further change in composition occurs.
This is analogous to a situation in which during a specific time interval, two students enter a crowded classroom and two leave. Change is occurring, but the number of students in the classroom is constant.
product-favoured, the amount of products is much higher than the amount of reactants.
reactant-favoured, the amount of reactants is much higher than the amount of products.
reactant-favoured, the amount of reactants is much higher than the amount of products.
The equilibrium state of a reaction at a particular temperature is characterised by a number known as the equilibrium constant (K) that is independent of how the equilibrium system was prepared.
Product-favoured reactions have very large K (greater than 100).
Reactant-favoured reactions have very small K (less than 10–2).
Reactions having intermediate K have significant amounts of both products and reactants at equilibrium.
Reactant-favoured reactions have very small K (less than 10–2).
Reactions having intermediate K have significant amounts of both products and reactants at equilibrium.