Reverse Reactions and Equilibrium Flashcards
Types of systems
open
closed
open system
systems that allow matter and energy to be exchanged with the surroundings
e.g. open water bottle
closed system
systems that allow energy, but not matter, to be exchanged with the surroundings
e.g. closed water bottle
Reversible reactions
Not all reactions go to completion
In some reaction systems (which will only ever be closed systems) there will always be a mixture of reactants and products
Reversible reactions example
H2O(l) -> H2O(g) & H2O(l) <- H2O(g)
Initially the reverse reaction rate is zero but as the concentration of the gaseous water increases the reverse reaction will take place
Dynamic equilibrium
A reversible reaction in a closed system will eventually reach dynamic equilibrium
The rate of forward reaction is equal to the rate of reverse reaction and the concentrations remain constant, not equal
It is equilibrium because the concentrations are constant and it is dynamic because the reactions will continue at the same rate in both directions
Reaction rate and concentration of example diagram
see onenote (diagrams) 1 and 2
Equilibrium constant
While the concentration of all reactants and products remain constant at dynamic equilibrium in a closed system, the relative concentrations is different for different systems
The equilibrium constant gives a value at a given temperature for a certain reaction and will not change if the temperature changes
calculating the equilibrium constant
Kc = products/reactants
each chemical is placed in square brackets to show its talking about concentration.
any coefficients of the chemicals are placed as indices
important notes about calculating Kc
PURE SUBSTANCES (water) OR CHEMICALS THAT CONCENTRATION CANNOT BE MEASURED (solids) ARE NOT INCLUDED IN Kc
LARGE values of Kc = favours PRODUCTS
SMALL values of Kc = favours REACTANTS
The K value WILL change with temperature
