10 [Equilibrium] Flashcards
(25 cards)
What is a irreversible and reversible reaction?
When hydrogen and oxygen react water is produced at the end there is little h2 or o2 remaining so this is a irreversible reaction.
Most combustion reactions due to being highly exothermic.
In organic chemistry reactions may not go onto completion, detectable amount of the reactants remained mixed with the products called reversable.
What is the decision for if a reaction if reversible?
How carefully concentrations of reactant and products. Reaction between HCl and NaOH goes to completion. Both acid and alkali are completely ionised. Pure water has electrical conductivity resulting from ionisation of the water molecules.
Indicating a reverse reaction is taking place. If a reaction is more than 99% complete then it is not reversible
What does the reaction between hydrogen and iodine show?
About 90% of the hydrogen and iodine react to form hydrogen iodide. 10% of hydrogen and iodine will remain unreacted no matter how long the reaction mixture is left for.
This is known as a forward reaction, the decomposition of hydrogen iodide to iodine is the backwards reaction
How is equilibrium established?
When the mixture of hydrogen and iodine is heated, the 2 gases start to react and form hydrogen iodide. Increasing time the concentration of the 2 reactants decrease so rate of forward reaction decreases.
Soon as HI is formed is starts to slow down and decompose, with increasing time the concentration of hydrogen iodide increase so the rate of backward reaction increases.
Eventually forward and back become equal at this point no further change in concentration in equilibrium. dynamic equilibrium.
What are the characteristics of the dynamic equilibrium graph?
Both forward and backward reactions are continuously occurring
The rate of forward reaction is equal to the rate of backward reaction
The concentrations of the reactants and products remains constant
What are the conditions that must be met for dynamic equilibrium to occur?
The reaction must be reversible
The reaction mixture must be in a closed container
How can the composition of an equilibrium mixture be changed?
When reaction mixture reaches equilibrium composition of mixture doesn’t change unless conditions remain the same.
What are the factors which affect the position of equilibrium of a reaction mixture?
Concentration of a component
Pressure of the system
Temperature of the system
Addition of a catalyst
What are the effects of a change in concentration?
Increasing concentration of one of the reactants in a system in equilibrium the rate of the forward will increase as more products will. As concentration of products increases rate of backwards reaction increases and a new equilibrium will be established. Moved to the right slightly more products formed
If concentration is decreased equilibrium moves to the left.
What is the effect of a change in pressure on equilibrium?
the effect of pressure only applies to reversible reactions involving gases. At a given temperature, the pressure of gas a gaseous mixture depends on number of gas molecules in a given volume. The pressure of a gaseous mixture may be increase by reducing the volume and reduced by increasing the volume.
How can the pressure at which a reaction is carried out be changed?
Increased by initially using more moles of reactant in the same volume.
Decreased by using less moles of the reactant same volume
Effect of a change in pressure caused by changing the volume of the reaction mixture studied using a gas syringe effect depends on the total number of moles on each side of equation.
What is the effect of change in pressure on equilibrium
More moles of reactants and less of products equilibrium goes to right
Fewer moles of reactants and more moles of products leads to equilibrium shifting to left
What would a graph show of an increase in pressure?
Graph shows higher pressure the more ammonia there is in the equilibrium mixture formed.
What is the effect of a change in temperature on equilibrium?
If temperature of an equilibrium mixture is raised, the rates of both forward and backward reactions will increase. Increase in the rate of endothermic reaction will be greater than the increase in the exothermic reaction. An increase in temperature will shift equilibrium in direction of the endothermic reaction.
Change in equilibrium depends on forward reaction is exothermic or endothermic
What is the effect of an increase or decrease in temperature being exo or endothermic reaction on equilibrium?
Temperature increase when forward reaction is exothermic leads to right
Temperature decrease when the forward reaction is exothermic leads to left
Opposite for endothermic
What is the effect of the addition of the catalyst on the position of equilibrium?
If a catalyst is added to the reaction mixture that is in equilibrium the rate of the forward and backward reaction will increase. Increase in rate will be the same for both reaction endo and exo so position of equilibrium is not altered.
It shortens time for equilibrium to be obtained.
What are the limits of making qualitative predictions?
arguments used on explaining the impacts of pressure, temperature and concentration are predictions not explanations why the changes occur. It is impossible to predict sometimes.
What is a Homogeneous system?
A system in which all the components are in the same phase like gas phase or aqueous
H2(g) + I2(g) >< 2HI(g)
What is a heterogenous system?
At least 2 different phases are present
CACO3 >< CaO + CO2 2 solid one gas
What is equilibrium law?
aA + bB >< cC dD
Known as equilibrium law
Important for writing the equilibrium constant concentration on right hand side are written in the numerator and concentration on right hand side on the donominator
How are reaction rates and reversibility important to industrial process?
Principle of reaction rates and reversibility play an important roe in the design and conditions for many industrial processes. In order to maximise profits it is about converting reactants into the products as quickly and completely as possible.
First problem is associated with kinetics next reversibility.
What is the Haber process?
Ammonia is manufactured in industry by direct synthesis of nitrogen and hydrogen.
N2 + 3H2 >< 2NH3
If reaction mixture used to reach equilibrium maximum yield of ammonia obtained from a low temp and a high pressure.
Reaction mixture does not reach a position of equilibrium in reaction chamber
What are the conditions for the Haber process?
Typically 450 degrees and 250 atmospheres. If reaction mixture was to reach equilibrium then the yield of ammonia would be over 30% practice yield of approximately 15% reaction mixture does not remain in the reaction chamber long enough for equilibrium to be established.
Why are the conditions 450 and 250atm?
Reaction between N2 and H2 is extremely slow at room temperature, largely because of the strong nitrogen triple bonds. Producing a high activation energy for the reaction. Even at high temperatures rate of reaction is low in absence of suitable catalyst.
Catalyst does not function very efficiently at low temperatures, relatively high temperature is necessary. A very high temperature is uneconomical extra energy cost. Decrease yield since increase in rate of backward reaction will be greater than the increase in rate of forward reaction
Under these conditions actual yield is about 50% of equilibrium yield. Low pressure means lower yield. In order to increase efficiency of the process unreacted nitrogen and hydrogen are fed into the reaction chamber mixed with fresh nitrogen and hydrogen.
