Unit 4- Equilibria Flashcards
What is a dynamic equilibrium?
- When events occur to maintain an equilibrium in a closed container
What is the general equilibrium constant for the standard reaction aA + bB –> cC + dD
Kc=([C]c x [D]d)/ ([A]a x [B]b)
What does the equilibrium constant represent?
The relationship between the molar concentrations of the reactants and products
What is a homogenous equilibria?
When the reactants and products are in the same phase e.g. water or liquid
What is a heterogenous equilibria?
when the states of the products and reactants differ
When an equilibrium constant is used, other than concentration , what can be used?
partial pressure
What is the partial pressure?
the pressure that the gas would have if the gas occupied the volume alone
How to calculate partial pressure?
(Number of moles of the substance/total moles in the mixture) x total pressure
How to calculate total pressure?
The sum of the partial pressure
What is different in a heterogenous equilibria for the constant?
Substances in the solid state are not considered as their concentrations is always constant
What is formula for the Partition constant? and where does it apply?
- For immisicible liquids
- Kpart = Concentration in liquid/concentration in water
- e.g. when iodine is added to water and hexane
- Kpart =[I] in hexane/ [I] in water
What is the link between the entropy of a system and the equilibrium constant?
Delta S = RlnK where K can be Kc or p and R the gas constant
What does a change in temperature in the equilibria affect?
- Ssurroundings
- Ssurroundings = -H/T
- Change in T affects Ssurroundings
- Affects Stotal as Stotal = Ssurroundings + Ssystem
What does the equilibrium constant measure?
How far a reaction goes to completion
If the value of the equilibrium constant is greater than 1x1010 , what does this represent?
The reaction has gone nearly to completion. Only small amount of reactant left
If the value of K is 1, what does this mean?
Concentration of reactants and products is roughly the same at equilibrium
If the value of K is smaller than 1x10-10, what does this mean?
The reaction hardly occurs, small amount of products formed
How does the size of the equilibrium constant affect the shift in equilibrium?
- Large K –> shifts right due to more products and less reactants
- Small K–> shifts left due to more reactants and less products
Does the equilibrium constant affect rate?
no, no effect