Reactivity 2.3 (SL) Flashcards
Dynamic equilibrium
When a rxn reaches equilibrium the rxn doesn’t stop, but the rate of the forward rxn is equal to the rate of the reverse rxn, so the equilibrium concs of the reactants and products remains constant.
When the value of K is large (>100)…
The reaction has virtually gone to completion and the concn of reactants in the equilibrium mixture is very small
When the value K is small (<0.01)…
The reaction has hardly proceeded and the concn of the the products in the equilibrium mixture is very small
If the value of K is in the range of 1 (between 10^-2 and 10^2)…
There will be appreciable amounts of both products and reactants in the equilibrium mixture
Equilibrium constant symbol and units
Symbol: K
Units: No units
What is the equilibrium constant for the reverse rxn
The reciprocal of the constant for the forward direction
How do the rates of the forward and backward reactions compare at equilibrium?
They are equal
Dynamic equilibrium
The rxn has not stopped, but both forward and backward reactions are occurring at the same rate
Equilibrium can be reached from either direction
This is because the same equilibrium rxn will result under the same conditions. No matter whether the rxn is started with all reactants, all products or a mixture
Effect on macroscopic (observable) properties at equilibrium
No effect, they stay the same as they depend on concs and components of the mixture (which are staying the same)
The concentrations of reactant and product are ____ but not ____ at equilibrium
constant, equal
Equilibrium position
The proportion of reactant and product in the equilibrium mixture.
The equilibrium position of reactions thats mixtures contain predominantly products are said to…
Lie to the right
The equilibrium position of reactions thats mixtures contain predominantly reactants are said to…
Lie to the left
What are the factors that effect the position of equilibrium?
- Concentration
- Pressure
- Temp
- not the addition of a catalyst
Le Chatelier’s Principle
A system at equilibrium when subjected to a change will respond in such a way as to minimize the effect of the change. (Whatever you do the system at equilibrium, the system will respond in the opposite way)
Why does the addition of a catalyst not affect the position of equilibrium?
The catalyst affects both the forward and reverse rxns equally. The catalyst will help the system to reach equilibrium faster though.
What conc changes would cause an eq shift to the left?
Inc in conc of product or dec in conc of reactant
How would you manipulate K when reversing the rxn?
take its reciprocal
How would you manipulate K when adding two rxns together?
Multiply the K value of each rxn together
How would you manipulate K when doubling all the coefficients in a rxn?
Square K
How would you manipulate K when halving all the coefficients in a rxn?
Square root K
How do industrial facilities increase the yield of product?
By removing product as it forms, forcing equilibrium to be continuously pulled to the right
When there is no overall volume change during a reaction and pressure is inc/dec what is the effect on the equilibrium position?
It will have no effect on the equilibrium position as the products and reactants will be affected equally.
When the volume decreases during a reaction and pressure is inc/dec what is the effect on the equilibrium position?
The equilibrium position is shifted towards the product side (the side with less volume) to minimise the increased pressure.
What type of rxn is heat a product in?
Exothermic
How to move equilibrium position to the product side of an exothermic rxn?
Removing heat (product) by lowering the temp
How to move equilibrium position to the product side of an endothermic rxn?
Increasing temp
For exothermic rxns the higher the temp the ___ the value of K
lower
For endothermic rxns the higher the temp the ___ the value of K
greater
Effect of Concentration on equilibrium position and change in value of K
Equilibrium position: changes
Change in K: no change
Effect of pressure on equilibrium position and change in value of K
Equilibrium position: changes if rxn involves a change in no. of gas molecules
Change in K: no change
Effect of temp on equilibrium position and change in value of K
Equilibrium position: changes
Change in K: changes
Effect of catalyst on equilibrium position and change in value of K
Equilibrium position: no change
Change in K: no change
When do Heterogenous Equilibria occur?
When one or more products or reactants is in a different pase to the other reactants and products.
Why do solids not appear in equilibria expressions?
Because they don’t have a concentration
