Chapter 2 Chemical Equilibrium ✓
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What makes a reaction reversible?
Its LOW activation energy
What makes a reaction non-reversible?
its HIGH activation energy
In which processes (physical or chemical) would you commonly see reversible reactions and give examples?
In physical processes such as, evaporation, condensation, dissolving, crystallising etc.
What is a closed system?
A closed system is where energy can enter or leave the system but not matter. A contained with a lid is an example.
What is an open system?
An open system is where both energy and matter can enter and leave the system. An unsealed flask is an example.
In what system (open or closed) is needed for a reversible reaction to reach equilibrium and why
A closed system because a closed system does not allow matter to enter or leave the system which allow equilibrium to be reached.
What happens during evaporation in an open system?
The vapour diffuses into the surroundings, leaving the system, which results in the flask becoming dry.
What happens during evaporation in a closed system?
The vapour is produced but cannot leave. It condenses and returns to the liquid phase within the flask
Why is evaporation and condensation in a closed system a reversible reaction?
Because water evaporates, then condenses, and the cycle continues.
What is dynamic equilibrium?
It is when the forward and reverse reactions occur at the same rate, leading to no observable change in the system.
What is equilibrium vapour pressure?
It is the constant pressure exerted by a vapour in equilibrium with its liquid phase.
What happens when a reversible reaction is in a closed system?
It reaches equilibrium, where forward and reverse reactions balance each other
What happens to the concentration of reactants and products at equilibrium?
They remain constant, but the relative concentrations of reactants and products differ between systems.
Do all systems have the same equilibrium composition?
No, some systems favour a high concentration of products, while others favour reactants.
What is the equilibrium constant (Kc)?
A numerical value representing the concentration of all species in a system at equilibrium.
Write down the general formula for the equilibrium constant expression
page 14
What do the coefficients in a balanced chemical equation represent?
The number of atoms or molecules involved in the reaction.
Which states of matter are included in the equilibrium constant expression?
Only gases (g) and aqueous (aq) species. Solids and liquids are excluded.
What is the only factor that will affect Kc?
Temperature
What does a large Kc value indicate?
The equilibrium favours products.
What does a small Kc value indicate?
The equilibrium favours reactants.
What does a Kc value close to 1 indicate?
Both reactants and products are present in significant amounts at equilibrium.
When can Kc be calculated?
When equilibrium has been reached
What is the reaction quotient (Qc)?
It measures the relative concentrations of reactants and products at any moment, not just at equilibrium.