7.4 Qualitative Changes To Equilibrium Flashcards
What happens when there’s a disturbance to equilibrium?
A new equilibrium will be established so that the rate of the forward reaction and reverse reaction is equal
What can disturb an equilibrium?
Pressure, temperature, concentration, or a combination of these
What is Le Chatelier’s Principle
When a chemical system at equilibrium is disturbed by a change in a property, the system will adjust to OPPOSE the change
What did Chatelier discover
That changing a property of a system creates a temporary “non equilibrium” state in the system, before a new equilibrium is established
How does ammonia synthesis use le Chatelier’s principle?
By increasing the pressure, equilibrium shifts to the right because it has fewer mols, so more ammonia is yielded
What happens to a chemical system if you increase pressure? decrease?
- Increase: equilibrium shifts to side with fewer mols
- Decrease: equilibrium shifts to side with more mols
What is an equilibrium shift
A change in concentration of reactants and products to restore an equilibrium state
What happens if you remove reactants
Reaction shifts left
What happens if you add reactants
Reaction shifts right
Explain how in Fe + SCN <-> FeSCN more product can be yielded
By adding more of a reactant one at a time (for example SCN), it will combine with Fe to create more products and vice versa. Adding a reactant will shift the rxn to the right to yield more product.
What happens if you remove a product
Reaction shifts right
What happens if you add product
Reaction shifts left
Define collision theory
Entities in a chemical system must collide to react
What happens when you increase concentration of an entity according to collision theory
It will most likely collide with other entities since there is more present
What kind of collisions can potentially contribute to a reaction
Collisions between reactant entities
The more frequently collisions occur, the more likely a…
Reaction will take place
What can collision theory tell us about a chemical reaction system
It can tell us how a system at equilibrium responds to changes in concentration
More reactant added = (collision theory)
More successful collisions; forward reaction increases, reaction shifts right
More product added = (collision theory)
More successful collisions; reverse reaction rate increases, reaction shifts left
What does the rate of a chemical reaction reflect (collision theory
How often reacting entities are colliding (whether its reactants or products)
If you increase the concentrations of the reactants, what happens to the rate of the forward reaction and how does the system compensate
The rate of the forward reaction increases, leading to more products yielded until the reverse reaction rate begins to increase until both rates are equal. The new equal rate is how the new equilibrium is established
Why do chemical engineers use Le Chatelier’s principle
To get a reaction to shift right to yield more product
How is Chatelier’s used in:
3NO2 + H2O <-> 2HNO3 + NO
Since nitric acid is very useful, NO gets removed by reacting it with O2. Since its a product, the system shifts right so that more desired nitric acid is yielded
How is Chatelier’s used in:
CO + H2O <-> CO2 + H2
In the gasification of carbon, it creates usable hydrogen fuel. More reactants get added to maximize yield of H2
How is Chatelier’s used in:
Hb + O2 <-> HbO2
In the lungs, there is a high concentration of oxygen so the reaction shifts right to form HbO2 which gets pumped to the body cells with low concentrations of oxygen. The reaction shifts left so that the oxygen is released from hemoglobin for body cells to use.
How is oxyhemoglobin formed?
From oxygen binding to hemoglobin
What happens if an endothermic reaction loses energy?
The reaction is losing a reactant, so rxn shifts left and energy is released
What happens if an exothermic reaction loses energy?
The reaction is losing a product, so rxn shifts right to make more products
What happens if an endothermic reaction gains energy?
Reactant was added, rxn shifts right
What happens if an exothermic reaction gains energy?
Product was added, rxn shifts left
What is an ideal gas?
A hypothetical gas:
- made up of entities with no size
- travels in a straight line
- has no attraction to each other (no intermolecular forces)
- obeys all gas laws
What does Boyle’s law state
As the volume of a gas changes, the pressure changes proportionally
State example of Boyle’s Law
In a bicycle pump, decreasing volume of gas in the cylinder to a third of its size increases the pressure threefold
What is partial pressure
The pressure that a gas in a mixture of gases would exert if it occupied the whole volume alone
All the pressure in a bicycle pump is…
the sum of the partial pressures of the gases in the cylinder
In ammonia synthesis, which side has more partial pressure of gas and why
The reactants, because there is 4 mols on the reactants side and 2 on the products
If you reduce the volume of a container involved in NH3 synthesis, which change in concentration would be greater? why?
The change in concentration of reactants will be greater because it has more mols
If volume was reduced, where would equilibrium shift? What is the purpose of the equilibrium shift here?
Since pressure would increase, and pressure shifts reaction to the side with fewer mols, rxn shifts right to reduce pressure in the system
Why would we want to change an equilibrium system without affecting equilibrium position? Is it possible?
For efficiency and productivity of yielding desired products. Despite limitations on how much concentration, pressure, and temp can be changed, it is possible.
How does a catalyst change an equilibrium system without affecting equilibrium position
It increases the reaction rates of both the forward and reverse reaction so that products are yielded faster
How does an inert gas change an equilibrium system without affecting equilibrium position
Since inert gases are unreactive it will not enter a chemical rxn. Adding an inert gas to a gas mixture (with constant volume) increases pressure to regulate the system. And, since equilibrium depends on partial pressures and an inert gas doesn’t affect partial pressure, the equilibrium position is left unaffected.
What is an inert gas
A noble gas with low reactivity since it has a full valence shell
What happens to entities colliding with an inert gas? Does equilibrium shift?
It does not result in a chemical reaction but the inert gas can redirect the movement of the entity. The collision frequency of forward and reverse rxns remain unchanged so equilibrium does not shift
How does the state of reactants affect equilibrium
Equilibrium can only be affected by concentrations of entities in the same states of matter as the substances in the system
Why does solid iodine not have an affect on the equilibrium of::
H2 (g) + I2 (s) <-> 2HI (g)
We ignore solids and liquids when determining equilibrium because their concentrations are constant and do not affect the equilibrium expression.
If K > 1, what is favored?
Products
If K < 1, what is favored?
Reactants
What happens to K if temperature increases in an endothermic reaction
K increases
What happens to K if temperature increases in an exothermic reaction
K decreases
What is the dependent variable
It is what’s being affected in an experiment
Example: When adding HCl to determine the affect on CuCl2, CuCl2 is dependent because it is being affected
What is the independent variable
It is what’s being changed in an experiment
Example: When adding HCl to determine the affect on CuCl2, HCl is independent because we are testing its effect on CuCl2
What’s a control
The experiment setup without any changes
What happens to a system with equal mols of gas on each side if volume is changed
Pressure cannot be changed, so equilibrium remains unaffected
Are liquids and solids affected by pressure changes
No
Which way does a reaction shift if you add a catalyst
No shift, catalysts don’t affect equilibrium position
