7. Equilibrium Flashcards
Whta is dynamic equilibrium
Dynamic equilibrium: equilibrium at which forward and reverse reactions are happening
Rate of forward and reverse reaction are the same
What are the feautures of equilibrium state?
Concentrations are constant but reaction rates are the same
(conc not the same because of unproportional equilibrium constants)
What are the limitations of Kc?
It can only be calculated for homogenous equilibrium (reactants and products of same state) Kc=[a]a[B]b/[C]c[D]d
For heterogenous equilibrium - Kc calculate from deltaG = -RTlnK
How is equilibrium constant Kc calculated form experimental data?
Kc changes with temperature
For what is the reaction quotient Q used?
Allows to identified which reaction forward or reverse is favoured not at equilibrium
How does invertingin teh reaction, changing conc and adding reactions changes Kc?
Manipulations can be done:
State Le Chatelier’s principle
Le Chatelier’s principle: when a system at equilibrium is disturbed, it will respond to minimise the effect of the change (will respond in the opposite way)
How does a catalyst affect both the forward and the reverse reaction?
No effect on Kc - just equilibrium reached faster
What are the factors which can affect the position of reaction and Kc?
What are the industrial reactions which are based on equilibrium?
- Haber process
- Contact process
- Production of methanol
Explain Haber process
N2 + 3 H2 -> 3 deltaH = - 93 kJ mol
Optimum conditions:
- NH3 removed as it forms - increases yield
- high pressure 2X107
- moderate temp 450C (exoth)
- catalyst: powdered iron, ruthenium (catalyst increases the rate of both forward and reverse reactions)
Explain Contact process
2 SO2 + O2 -> 3 deltaH = -196kJ mol
Optimum conditions:
Explain production of methanol
CO + 2 H2 -> 3OH deltaH = -90 kJ mol
Ideal conditions:
What value of Gibbs free E says about the reaction?
What is the free E change when equilibrium is being established? (forward reaction spontaneous)
What values are of G and S at equilibrium?
S - maximum (most entropy - most disorder)
G - minimum (lowest point at equilibrium)
What is the relationship between Kc and deltaG?
deltaG = -RT lnK
R - gas constant
T - temperature
lnK - natural log of Kc
How to calculate Q and Kc from a graph?
Until reaction rates are constant - no equilibrium - Q is calculated
When reaction rates are constant - equilibrium - Kc calculated
When Q approaches Kc from higher to lower (Q>Kc) - reaction procedes to the left
When Q approaches Kc from lower to higher (Kc>Q) - reactions proceeds to the right
When Q=Kc - equilibrium
