okay lets start..
Lately we have been learning about Chemical Equilibrium.
What we did last class was learn about "Le Chatelier's Principle"
This principle states that "When the system at equilibrium is subjected to stress, the system will adjust so as to relieve the stress."
Changing of Concentration
In a system, a change in the concentration of products or reactants present at the equilibrium, combine to form a stress. At equilibrium, the ratio of products to reactant concentrations is constant.
When adding more reactant or removing of the products, it would upset the equilibrium.
To relieve the stress, you need to form more of the products or use up the reactant.
note:
a) Increasing the concentration of a reactant shifts an equilibrium to the products (or right hand) side because the rate of the forwards reaction is increased.
b) Increasing the concentration of a product shifts an equilibrium to the reactant (or left hand) side because the rate of the reverse reaction is speeds up.
c) Decreasing the concentration of a reactant (by removal or by compounding it with something else of by precipitation) shifts an equilibrium to the reactants (left hand) side because the forwards reaction is slowed down. The reverse reaction will 'overtake' the forwards reaction.
d) Decreasing the concentration of a product shifts an equilibrium to the products (right hand) side because the reverse reaction is slowed and the forward reaction 'overtakes'.
Pressure Changes
N2O4(g) <----- ----->2NO2(g)
Very light yellow, almost colorlesss Brown
Increases pressure will cause more collisions to take place between gaseous molecules (pressure is a measure of the number of particles per unit volume).
- An increase in pressure will favour the reaction involving the most particles.
- An increase in pressure favours 2NO2 molecules reacting more than one N2O4 reacting.
- The reverse reaction speeds up.
- The equilibrium shifts to the left hand side. Ex. A lighter color is produced, after an expected initial darkening caused by the original color being 'compressed'.
Pressure changes only matter if there is a different number of gas molecules on each side. Pressure changes are irrelevant if there are no gas molecules in the reaction.
Ex.
H2(g) + I2(g) <---- ----> 2HI(g)
There is no change in Equilibrium position.
Temperature Change
An increase in temperature speeds up an reaction. An endothermic reaction is helped more by a temperature rise than an exothermic reaction.
Endothermic
N2O4(g) <--------- ---------> 2NO2(g)
Dinitrogen tetaoxide Exothermic Nitrogen Dioxide
( very light yellow, colorless ) ( brown )
- Increasing temperature will favour the forwards reaction more so that the reverse, and so the color darkens and the equilibrium shifts to the right hand side.
- Decreasing temperature slows the endothermic reaction the most, and so the forward reaction slows drastically and the reverse reaction wins, which means that the color lightens as the equilibrium shifts to the left side.
A catalyst makes an easier path for the reaction, the path for the reverse reaction is made equally easier. A catalyst will not shift an equilibrium position because both rates are equally increased. The equilibrium is achieved quicker in time and under easier conditions.
However,
If a catalyst is added to a system which is not at equilibrium, the system will reach equilibrium much quicker since forward and reverse reaction rated are increased.
Well, I think that's basically what we learned on Monday.
Remember to do all your worksheets and have a good day everyone!
The next scriber will be..... ARI5 ! =)
