Equilibrium Flashcards
What is a system?
A chemical reaction can be considered a system. Everything else around the system is considered the surrounding
Explain endothermic reactions in a system.
in an endothermic reaction, energy is absorbed into the system from the surrounding
Explain exothermic reactions in a system.
in an exothermic reaction, energy is emitted to the surrounding from the system
What is an open system?
An open system is the most common of the two, matter and energy can be exchanged between the system and the surroundings.
What is a closed system?
A close system is a reaction where energy can be exchanged but cannot exchange matter with the surrounding.
What is an irreversible system?
reactions that occur in one direction or where the products cannot be reverted back to the reactants are described to be non-reversible or irreversible reactions
What is a reversible system?
some reactions are reversible meaning the products, once formed, can react again to re-form back into the reactant counterparts
Explain the reversible system of evaporation and condensation of water.
- water can cycle between the different phases as each process is reversible- these changes can occur in either open or closed systems
- in a closed system, the water vapour cannot escape
- reversible reactions in a closed system eventually reach a point where the forward and reverse reaction rate are equal
- there will be no further changes to the observer at this point
- the system has reached a state of equilibrium
- on the other hand, in an open system, the forward and reverse reaction rate are not equal as the condensed water molecules are able to escape the system
- this means equilibrium will never be achieved in an open system
Explain the reversible system of saturated sugar solutions
- consider a saturated solution of sugar in contact with undissolved sugar at a constant temperature
- the sugar molecules are dissolving at the same rate as they are crystallising and the mass of the sugar crystals is presented to be constant
- this process is reversible and in equilibrium
- even though there is no lid in the system, this type of reaction can be considered a closed system as no gas is involved therefore having no reactant loss during the process of the reaction, no loss of reactants or product molecules to the surroundings
Explain the reversible system of Haemoglobin and Oxygen gas
- haemoglobin is a large protein molecule that is the pigment in red blood cells
- is responsible in transferring oxygen from your lungs to the blood cells in our body
- when we inhale, oxygen from the air combines with haemoglobin to form oxyhaemoglobin
- the reaction between oxygen and haemoglobin is reversible
- the oxyhaemoglobin is transported through the blood system to other cells in the body where oxygen and haemoglobin is released
- the oxygen is then used for respiration which means this reaction is reversible
- although this reaction can be considered an open system, an equilibrium is established in the blood as it flows through the body
- at this point, it can be considered a closed system as no reactants or products are loss to the surroundings
How do you explain reversibility?
- the reversibility of a reaction can be understood by referring to an energy profile diagram
- when particles collide, the energy associated with collisions can break the bonds in the reacting particles to form new products
- the energy to break these bonds are known to be the activation energy
- once the product is formed, it is possible to reverse this reaction
- if the newly formed product particles collide with enough energy to overcome or equal the activation energy of the reverse reaction, it is possible to re-form the original reactant
- if the forward reaction is endothermic, the reverse reaction would be exothermic
Explain equilibrium.
in reversible reactions, the formation of products as a result of reactants colliding is not the end, some of the products particles once formed have enough energy to collide and re-form the reactants
Give an example explaining equilibrium.
- itrogen and hydrogen gas molecules collide to form ammonia, this can be represented as the forward reaction N2 (g) + 3H2(g) → 2NH3 (g)
- as this reaction proceeds, the concentration of nitrogen and hydrogen gas particles decrease so the frequency of collisions of nitrogen and hydrogen gas particles decrease and the rate of production of ammonia decreases
- at the same time ammonia is being produced, some ammonia molecules collide and decompose to re-form nitrogen and hydrogen gas 2NH3(g) → N2(g) + 3H2(g)
- eventually, the forward and reverse reaction proceeds at equal rates, when this happens, ammonia is formed at exactly the same rate as it is breaking down
- the concentration of ammonia, nitrogen and hydrogen will then remain constant
- to an observer, the reaction now appears to have stopped with nothing changing
- in a closed system with constant pressure, temperature no further changes will occur, the reaction has reached a point of equilibrium
What is dynamic state of equilibrium
chemical equilibrium can be described to be a dynamic state because the forward and reverse reaction have not ceased, instead occur simultaneously at an equal rate
what happens during dynamic state of equilibrium
- the macroscopic properties are constant, meaning the amount and concentration of reactants and products, the pressure and temperature are constant
- the reaction is “incomplete” and all of the substances are present in the equilibrium mixture
- at the molecular level, the bonds are constantly being broken and new bonds are formed as the reactants and products continue to be converted from one to another
How is dynamic equilibrium reached?
dynamic equilibrium is reached either through physical or chemical reactions taking place in a closed system
