Chemistry module 5 Equilibrium

Inquiry Question 1: Static and Dynamic Equilibrium

What happens when chemical reactions do not go through to completion?

Static equilibrium

A state where no chemical reactions are occurring because the forward and reverse reaction rates are both zero.

Dynamic equilibrium

A state in a closed system where the forward and reverse reactions occur continuously at equal rates, resulting in constant concentrations of reactants and products.

Chemical equilibrium

A dynamic state where the forward and reverse reactions occur at equal rates in a closed system.

Forward reaction

The reaction that converts reactants into products.

Reverse reaction

The reaction that converts products back into reactants.

Reversible reaction

A chemical reaction that can proceed in both the forward and reverse directions under the same conditions.

Irreversible reaction

A chemical reaction that proceeds essentially to completion and cannot readily reverse under the same conditions.

Closed system

A system that allows the transfer of energy but not matter between the system and its surroundings.

Open system

A system that allows the transfer of both energy and matter between the system and its surroundings.

Macroscopic constancy

The observable properties of a system, such as colour, pressure and concentration, remain constant at dynamic equilibrium.

Activation energy

The minimum energy required for reacting particles to undergo a successful collision.

Reaction rate

The change in concentration of reactants or products per unit time.

Collision theory

A theory stating that chemical reactions occur when particles collide with sufficient energy and correct orientation.

Successful collision

A collision with enough energy and correct orientation to form products.

Entropy

A measure of the disorder or randomness of a system.

Enthalpy (ΔH)

The heat energy absorbed or released during a reaction at constant pressure.

Non-equilibrium system

A system in which the forward and reverse reaction rates are unequal, causing concentrations to change over time.

Combustion

An irreversible, exothermic reaction in which a substance reacts rapidly with oxygen to produce heat and light.

Photosynthesis

An endothermic process that converts carbon dioxide and water into glucose and oxygen using light energy.

Inquiry Question 2: Factors Affecting Equilibrium

What factors affect equilibrium and how?

Le Chatelier's Principle

When a system at equilibrium is disturbed, it shifts to oppose the disturbance and establish a new equilibrium.

Equilibrium position

The relative amounts of reactants and products present at equilibrium.

Disturbance

A change to an equilibrium system caused by altering concentration, pressure, volume or temperature.

Concentration

The amount of solute present in a given volume of solution, usually measured in mol L⁻¹.

Increasing concentration

Adding more of a reactant or product causes the equilibrium to shift to consume the added substance.

Decreasing concentration

Removing a reactant or product causes the equilibrium to shift to replace the removed substance.

Volume

The amount of space occupied by a gas.

Pressure

The force exerted by gas particles colliding with the walls of a container.

Increasing pressure

Caused by decreasing volume, favouring the side of equilibrium with fewer moles of gas.

Decreasing pressure

Caused by increasing volume, favouring the side of equilibrium with more moles of gas.

Temperature

A measure of the average kinetic energy of particles.

Exothermic reaction

A reaction that releases heat to the surroundings (ΔH < 0).

Endothermic reaction

A reaction that absorbs heat from the surroundings (ΔH > 0).

Effect of increasing temperature

The equilibrium shifts towards the endothermic reaction to absorb the added heat.

Effect of decreasing temperature

The equilibrium shifts towards the exothermic reaction to replace the lost heat.

Catalyst

A substance that increases the rate of both forward and reverse reactions by lowering activation energy without being consumed.

Effect of a catalyst on equilibrium

A catalyst speeds up the attainment of equilibrium but does not change the equilibrium position or the value of Keq.

Inert gas

A gas that does not react with any species in the equilibrium system.

Effect of an inert gas

Adding an inert gas at constant volume has no effect on the equilibrium position.

Pure solid

A solid whose concentration remains constant and is therefore omitted from equilibrium expressions.

Pure liquid

A liquid whose concentration remains constant and is therefore omitted from equilibrium expressions.

Gas moles

The total number of moles of gaseous particles in a balanced chemical equation used to predict pressure effects on equilibrium.

Inquiry Question 3: Equilibrium Constant

How can the position of equilibrium be described and what does the equilibrium constant represent?

Equilibrium constant (Keq)

A constant that describes the ratio of equilibrium concentrations of products to reactants, each raised to their stoichiometric coefficients.

Equilibrium expression

The mathematical equation used to calculate the equilibrium constant.

Homogeneous equilibrium

An equilibrium in which all reactants and products are in the same physical state.

Stoichiometric coefficient

The number placed before a chemical formula indicating the mole ratio in a balanced equation.

Equilibrium concentration

The concentration of a substance after equilibrium has been established.

Initial concentration

The concentration of a substance before the reaction begins.

RICE table

A table used to determine equilibrium concentrations by organising Initial, Reaction, Change and Equilibrium values.

Reaction quotient (Q)

The ratio of product concentrations to reactant concentrations at any stage of a reaction.

Q = Keq

The system is already at equilibrium.

Q < Keq

The forward reaction is favoured until equilibrium is established.

Q > Keq

The reverse reaction is favoured until equilibrium is established.

Large Keq

A value much greater than one indicating products are favoured at equilibrium.

Small Keq

A value much less than one indicating reactants are favoured at equilibrium.

Temperature effect on Keq

Temperature is the only factor that changes the value of the equilibrium constant.

Concentration effect on Keq

Changing concentration alters the equilibrium position but not the value of Keq.

Pressure effect on Keq

Changing pressure alters the equilibrium position for gaseous systems but not the value of Keq.

Volume effect on Keq

Changing volume alters the equilibrium position but not the value of Keq.

Reaction mechanism

The sequence of elementary steps by which reactants are converted into products.

Inquiry Question 4: Solution Equilibria

How does solubility relate to chemical equilibrium?

Solution equilibrium

A dynamic equilibrium established between dissolved ions and undissolved solid in a saturated solution.

Dissolution

The process in which a solute dissolves in a solvent to form a solution.

Solute

The substance that is dissolved in a solvent.

Solvent

The substance that dissolves the solute.

Solution

A homogeneous mixture consisting of one or more solutes dissolved in a solvent.

Solubility

The maximum amount of solute that can dissolve in a given quantity of solvent at a specified temperature.

Unsaturated solution

A solution capable of dissolving more solute at a given temperature.

Saturated solution

A solution containing the maximum amount of dissolved solute at a given temperature.

Supersaturated solution

A solution containing more dissolved solute than normally possible at a given temperature and is unstable.

Ion-dipole force

The electrostatic attraction between an ion and the partially charged end of a polar molecule.

Hydration

The process by which water molecules surround dissolved ions.

Hydration sphere

A layer of water molecules surrounding a dissolved ion.

Dissociation

The separation of an ionic compound into its constituent ions when dissolved in water.

Precipitation

The formation of an insoluble solid from aqueous ions.

Precipitate

An insoluble solid formed during a precipitation reaction.

Solubility product constant (Ksp)

The equilibrium constant for the dissolution of a sparingly soluble ionic compound.

Ksp expression

The mathematical expression relating the concentrations of dissolved ions in a saturated solution.

Reaction quotient (Qsp)

The ionic product calculated using current ion concentrations before equilibrium is established.

Qsp < Ksp

More solid can dissolve because the solution is unsaturated.

Qsp = Ksp

The solution is saturated and at equilibrium.

Qsp > Ksp

A precipitate forms because the solution is supersaturated.

Common ion effect

The decrease in solubility of an ionic compound caused by the addition of an ion already present in solution.

Solubility equilibrium

A dynamic equilibrium between dissolved ions and undissolved solid in a saturated solution.

Double displacement reaction

A reaction in which positive and negative ions exchange partners to form new compounds.

Solubility rules

A set of guidelines used to predict whether an ionic compound will dissolve or form a precipitate in water.