P- Equilibria (P2) Flashcards
What is the Le Chatelier’s principle used for?
predict effects of changes in:
1. temp
2. pressure
3. conc
on the position of equilibrium in homogeneous reactions
What happens in a reversible reaction at equilibrium?
- forward and reverse reactions proceed at equal
rates - the conc of reactants and products remain constant
Does a catalyst affect the position of equilibrium?
x
Does a reversible reaction ever go to completion?
NO
Condition for equilibrium to occur
closed system
What is the Le Chatelier’s principle?
- if conditions of equilibrium changed
- position shifts to oppose the change
What are the 2 types of reversible reactions?
- Homogeneous- everything in same phase (eg. all gas)
- Heterogenous- things present in more than 1 phase (eg. solids & gases)
What does Kc stand for + what is it proportional to?
- K- equilibrium constant; c- conc.
- Kc ~ products/ reactants
- large when eq. lies on the RHS
State how, and explain why, the use of a catalyst might or migth not change the equilibrium yield of the product, and also the amount of product produced, in a given time. (4)
- x change in eq. yield
- ↑ rate of both (forward + reverse) reactions equally
- amount of product ↑ ∵ rate↑
What does k represent?
rate constant
What is Kc ?
Ratio of conc. of products to reactants in an equilibrium system
What are the features of Kc for a reaction ?
- diff. for every reaction at given temp.
- constant for a reaction at constant temp.
How do you calculate Kc ?
eg. H2 + I2 ⇌ 2HI
[HI]²
Kc = ——————-
[H2] [I2]
- [ ] = conc. (mol/dm3)
x units in this case ∵ same no. of moles on both sides
How do you calculate Kc ?
eg. H2 + I2 ⇌ 2HI
[HI]²
Kc = ——————-
[H2] [I2]
- [ ] = conc. (mol/dm3)
x units in this case ∵ same no. of moles on both sides
What affects the value of Kc?
temp only
x pressure/ catalyst
