Equilibria Flashcards
What happens in a reversible reaction?
The products can react to produce the original reactants
Describe why the rate of the forward and backward reaction changes during reversible reactions
As reactants react, their concentrations fall, so the forward reaction will slow down as more products re made their concentrations rise, the backward reaction will speed up
What is a closed system?
no reactants are added, no products are removed
What happens when a reversible reaction happens in a closed system? (describe what a dynamic equilibrium is)
Initially, as the reaction proceeds, the concentration of reactants decreases, while the concentration of products increases. However, as the forward reaction continues, the rate of the reverse reaction also increases because the concentrations of the products are increasing. Eventually, the rates of the forward and reverse reactions become equal, and the system reaches dynamic equilibrium.
When a dynamic equilibrium is eventually achieved = the rate of the forward reaction is equal to the rate of the backward reaction = concentrations of reactants and products have reached a balance and won’t change (the concentrations are CONSTANT)
- This doesn’t mean that the amounts of reactants and products are equal
What does it mean when the equilibrium lies to the left/right?
right = concentration of products are greater
left = concentration of reactants greater
What is le chatelier’s principle?
if a system at equilibrium is subjected to a change, the equilibrium tends to shift, so as to oppose the effect of that change
What happens when the temperature of a system at equilibrium is increases or decreases in an EXOTHERMIC reaction and why?
- decrease = increased yield as the equilibrium will move in the exothermic direction to produce more heat
increase = will move to the endothermic reaction to reduce heat, reduces yield
What happens when the temperature of a system at equilibrium is increases or decreases in an ENDOTHERMIC reaction and why?
increasing temp = increase yield as the equilibrium will move in the exothermic direction to produce less heat
decreasing = decreases yield, move to the exothermic direction to produce more heat.
What happens when pressure increases or decreases in an equilibrium reaction?
- an increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules
- a decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules
What happens when concentration increases or decreases in an equilibrium reaction?
If the concentration of one of the reactants or products is changed, the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again.
If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.
If the concentration of a product is decreased, more reactants will react until equilibrium is reached again.
What effect does catalyst have on equilibrium?
has no effect of equilibrium position
due to increasing the rate of reaction, equilibrium is achieved more quickly as it provides an alternate pathway for the reaction
increases the rate of the forward and backward reaction equally
What is Kc constant
A values that describes the state of equilibrium with respect to the concentrations of the reactants and the products
Which factor changes the Kc constant?
temperature
An experiment was carried out to determine the equilibrium constant, Kc, for the following reaction. CH3CH2COOH + CH3CH2CH2OH CH3CH2COOCH2CH2CH3 + H2O A student added measured volumes of propan-1-ol and propanoic acid to a conical flask. A measured volume of concentrated hydrochloric acid was added to the flask, which was then sealed. After 1 week, the contents of the flask were poured into water and the solution was made up to a known volume. This solution was titrated with standard sodium hydroxide solution.
(a) Explain how the student could determine the amount, in moles, of propan-1-ol added to the flask.
- Because we do not have the concentration, we need to find another to calculate the number of moles (Mr x mass)
- Multiply the volume of propan-1-ol by density to get the mass
- Divide mass by Mr of propan-1-ol
An experiment was carried out to determine the equilibrium constant, Kc, for the following reaction. CH3CH2COOH + CH3CH2CH2OH CH3CH2COOCH2CH2CH3 + H2O A student added measured volumes of propan-1-ol and propanoic acid to a conical flask. A measured volume of concentrated hydrochloric acid was added to the flask, which was then sealed. After 1 week, the contents of the flask were poured into water and the solution was made up to a known volume. This solution was titrated with standard sodium hydroxide solution.
b) The titration described above gives the total amount of acid in the equilibrium mixture. Explain how, by carrying out a further experiment, the student could determine the amount of propanoic acid in the equilibrium mixture.
Titrate a measured volume of concentrated HCl added initially to determine the moles of HCl.Subtract this number of moles of HCl from the total number of moles of acid at eqm
