Chemical Equilibria Flashcards
When is a system in equilibrium?
When the rate of the forward reaction is equal to the rate of the reverse reaction
When does a reaction system remain in equilibrium?
as long as the system is located (or closed)
What is a dynamic system?
one where reactants are being used up to form products and products are breaking down to form reactants but no change is observed in the reaction mixture; macroscopic properties (temperature and pressure) remain constant.
What is the position of equilibrium?
extent of a reaction when equilibrium is established
What are the features of a system at equilibrium?
-Rate of the forward reaction is equal to the rate of the backward reaction
-Concentration of reactants and products remains constant (*but is constantly moving)
-Systems are isolated
-Macroscopic properties remain constant (temp and pressure)
what are the two different types of equilibrium system?
Homogenous and Heterogeneous
What is heterogeneous equilibrium?
reactants and products are in different phases (states) (e.g. thermal decomposition) CaCO3(s)Heat⟶CaO (s)+CO2(g)
What is homogenous equilibrium?
reactants and products are in the same phase (state)
What is [A]?
concentration of chemical A in
moldm-3
What is Kc?
the equilibrium constant-product of the concentrations of products over the product of the concentrations of reactants gives a ratio and shows how far towards the right or left a reaction lies when a reaction is at equilibrium;
What are stoichiometric ratios used to give the the kc equations?
the power?
what type of equilibria doe kc deal
with?
homogeneous
what does the larger value for the Kc mean?
The more the reaction has gone to completion
what does a large kc greater than one mean?
products are “favoured”; equibrium lies towards the right.
what does a small Kc less than one mean?
reactants are “favoured”; equilibrium lies towards the left.
when will an equilibrium system only remain in equilibrium?
When it is isolated
What happens once the conditions of equilibrium are changed?
The system will no longer be in equilibrium
What are the conditions that affect equilibrium?
-temp
-pressure
-conc
What is Le Chatelier’s principal?
When a system under dynamic equilibrium is subjected to a change, the equilibrium will shift so as to oppose the change
what happens if the concentration of the reactants are increased? (in dynamic equilibrium)
They equilibrium shifts to the right hand side The yield of the product will increase
what happens when the concentration of products are decreased? (in dynamic equilibrium)
-The equilibrium shifts to the right hand side
-The yield of the product will increase
What are affected by change in pressure?
gases
what does an increase in pressure of an equilibrium mixture lead to?
the equilibrium moving so as to decrease the pressure.
-does this by decreasing the number of molecules. (Fewer moles = lower pressure so equilibrium shifts to the side with the least gas moles).
what does a decrease in pressure of the equilibrium mixture lead to?
the equilibrium mixture leads to the equilibrium moving so as to increase the pressure. It does this by increasing the number of molecules. (more moles = higher pressure so equilibrium shifts to the side with the most gas moles)
What will the temperature increased favour?
The endothermic reaction
what will the temperature reduced favour?
the exothermic reaction
what do catalysts do?
-reduce the activation energy of a chemical reaction and therefore cause reactions to be speeded up.
What does a catalyst do to the position of equilibrium?
does not affect the position of equilibrium however; it will affect the rate at which equilibrium is established
In industry why are theoretical conditions not always used and what are often used instead?
-these can prove to be uneconomical or lead to a slow rate of reaction
-compromise set of conditions are used to run the plant at a profit, whilst obtaining the best yield and rate.
-so theoretical conditions are modified
what does a low temperature lead to and why? (modification)
-very slow rate of attainment of equilibrium
-because the reaction has a high activation energy due to the strength of the triple bond which has to be broken before the nitrogen can react.
However a high temperature would lead to a poor yield as the position of equilibrium would move to the left
however what would a high temperature lead to? (composition)
a poor yield as the position of equilibrium would move to the left
what is the compromise condition for pressure?
-Very high pressure will increase the rate and also the yield but there is a significant increase in the cost of the plant.
-High specification pumps are required to maintain high pressure and maintenance of these is costly
how is the problem of low rate of reaction overcome?
by using a catalyst, which enables the reaction to occur, by a different route of lower activation energy
What else can increase the rate?
increasing the temperature and sacicing a high percentage yield
what happens on the formation of ammonia?
-ammonia is removed so that the system does not reach equilibrium
-increases rate of reaction
what are the conditions used in common ammonia plant?
200atm
450°C
what does 80% of ammonia production go into?
making fertiser such as ammonium sulfate
what are smaller proportions of ammonia used for?
The production of nitric acid which in turn is used to make explosives and polymers such as nylon which is a polyamide
what problems are associated with low/high pressure? (optimum theoretical conditions)
Low- Slow rate of reaction
High -Uses a large amount of energy/fuel, provides a safety risk
what problems are associated with low/high pressure? (optimum theoretical conditions)
Low- Slow rate of reaction
High- Uses a large amount of energy/fuel, Provides a safety risk, Uses a large amount of energy/fuel
