QCE Senior Chemistry U3: Equilibrium (QLD Teachers)

What can be changed in a reaction to alter the equilibrium position?

Concentration, temperature, pressure/volume (only applies to gases)

What happens to the equilibrium position when the product concentration is increased?

The reverse reaction increases and equilibrium moves to the left

What does Le Chatelier's principle state?

If an equilibrium system is subjected to a change, the system will adjust itself to partially oppose the effect of the change

What happens to the equilibrium position when the reactant concentration is increased?

The forward reaction increases and equilibrium moves to the right

On an equilibrium graph how do you know the reaction has reached equilibrium?

When equilibrium is established the concentration lines are horizontal

What is meant by an "open system"?

An open system allows matter and energy to be exchanged with the surroundings

Are all reactions reversible?

No, for example due to the formation of energetically stable products or loss of products into the environment

What is a "closed system"?

A reaction vessel that does not allow the reactant or product particles to escape

Give an example of an "open" system.

A flask with no lid that allows heat and gas products escape

What type of system is it when energy can escape but not matter?

Closed system

What is meant by the term "reversible reaction"?

Reactions in which the conversion of reactants to products and products to reactants occur simultaneously.

Are physical changes reversible?

Generally they are reversible as chemical bonds remain unchanged

Why is a substance in a system more likely to react when the temperature is higher?

The particles of that substance have more kinetic energy, causing them to collide more often with the other particles in the system, making the reaction occur

How are equilibrium reactions symbolised?

Equilibrium reactions are symbolised by ⇌

What is activation energy?

The minimum amount of energy required in the collision between reactants for a reaction to occur

What can you measure using observation in equilibrium reactions?

You can observe whether the forward or reverse reaction has occurred if the reactants and products have different colours

In a reaction where a gas is produced what type of system is required for equilibrium to be reached?

A closed system

What does Kc represent?

The equilibrium constant

When is a state of dynamic equilibrium reached?

A state of equilibrium is reached when the rate of the forward and reverse reactions are equal

How can you measure the concentration of an equilibrium using pH?

You can measure the change in pH and calculate the H3O+ concentration, then use simple stoichiometry

Can forward and reverse reactions occur at the same time?

Yes, a forward and reverse reaction can occur at the same time if the reaction occurs within a closed system

What is the impact on the equilibrium position when a catalyst is added to a reaction in a closed system?

There is no impact on the equilibrium position. Equilibrium will only be reached faster

What concentrations are not included when calculating the equilibrium constant?

Concentrations of pure liquids and solids are not included, water is only included if it is a product such as in condensation reactions

Where can the elements with the lowest ionisation energy be found on the periodic table?

"Bottom left e.g. Cs, Rb, Ba"

What kind of ionisation energy makes elements lose electrons more readily?

Low ionisation energy

Is the equilibrium constant value largest when the concentration of reactants is larger than the products?

No

What energy is required to remove an electron from an element?

First ionisation energy

"True or False? The stronger the electronegativity, the more readily the element will accept electrons."

TRUE

If Kc is larger than 104 is there significantly more reactant or product?

Product

"True or false? Is the Kc of a reaction temperature dependent?"

TRUE

What does RICE stand for?

Reaction, initial concentration, change in concentration, equilibrium concentration

What happens to the equilibrium position for an endothermic reaction when heat is added?

The equilibrium position will move towards the product side as heat is stored in the molecule

What can you do to increase the concentration of gas in a closed system?

Decrease the volume