Le chatelier’s principles and stable and dynamic equilibrium

Irreversible Reactions

Reactions that proceed in one direction only from reactants to products.

Reversible Reactions

A reaction where the products can be converted back into its reactants. They can go both left and right indefinitely. Eventually the reaction appears to stop, however.

Dynamic Equilibrium

Reached when the rates of reaction for both the forward and backward reactions are the same.

Equilibrium

Refers to a state of balance. It can be static or dynamic.

Types of Equilibrium (state of balance)

Static, Dynamic

Static Equilibrium

When there is no movement/rate of reaction to maintain the state of balance. Therefore it is an unmoving equilibrium.

Example of Dynamic Equilibrium in a Physical System (Br2(l) ⇌ Br2(g), in a closed environment)

Initially, liquid particles vaporize at a high rate with the rate of condensation at a low rate. Eventually vaporization slows down and condensation occurs faster. Eventually both rates become equal. Equilibrium.

Types of Equilibrium (by phase)

Homogeneous, Heterogeneous

Phase

A homogeneous portion of matter.

Homogeneous Equilibrium

Reactants and products are in the same phase (state), e.g. H2(g) + I2(g) ⇌ 2HI(g).

Heterogeneous Equilibrium

Reactants and products are in different phases, e.g. CaCO3(s) ⇌ CaO(s) + CO2(g).

Graphical Representation of Dynamic Equilibrium

The curves become horizontal as the rate of reaction becomes equal between reactants and products.

Equilibrium Composition

The concentration of reactants and products at equilibrium.

Amounts/Rates at Equilibrium

The amount of each product/concentration does not have to be equal, only the rates of reaction.

Rate of Reaction in Dynamic vs Static Equilibrium

In dynamic equilibrium the rate is never zero, unless for static equilibrium. The rate of reaction stabilizes as the concentration does so.

Characteristics of Dynamic Equilibrium

Can only be obtained in a closed system; macroscopic properties remain constant; changes in temperature, pressure, volume and concentration can change the equilibrium position (catalysts do not); rate of forward reaction equals rate of reverse reaction; concentration is constant for reactants and products.

Closed System

A system that prevents atoms from being added or escaping the reaction.

Macroscopic Properties

Properties you can measure: colour, pH, [C]. They remain constant at equilibrium.

Effect of Catalysts on Equilibrium

Catalysts do not change the equilibrium position.

Le Chatelier's Principle

When a chemical system at equilibrium is stressed, the system works to restore equilibrium.

Stress (Le Chatelier's Principle)

Includes: change in pressure, change in temperature, change in concentration.

Factors in Le Chatelier's Principle

Concentration, Pressure

Concentration (Le Chatelier's Principle)

When concentration is changed, stress is placed on the equilibrium to shift to the side of lower concentration, causing the concentration of said side to increase until equilibrium is reached.

Pressure (Le Chatelier's Principle)

Pressure only affects reactions involving gases. The more pressure, the more molecules colliding and therefore the more reactants. When pressure is changed, stress is placed on the equilibrium to shift to the side of lower pressure, causing the pressure to increase on said side until equilibrium is reached. If only one side has gas molecules, the equilibrium will always shift to the side with no gas molecules.

Irreversible Reactions

Reactions that proceed in one direction only from reactants to products.

Reversible Reactions

A reaction where the products can be converted back into its reactants. They can go both left and right indefinitely. Eventually the reaction appears to stop, however.

Dynamic Equilibrium

Reached when the rates of reaction for both the forward and backward reactions are the same.

Equilibrium

Refers to a state of balance. It can be static or dynamic.

Types of Equilibrium (state of balance)

Static, Dynamic

Static Equilibrium

When there is no movement/rate of reaction to maintain the state of balance. Therefore it is an unmoving equilibrium.

Example of Dynamic Equilibrium in a Physical System (Br2(l) ⇌ Br2(g), in a closed environment)

Initially, liquid particles vaporize at a high rate with the rate of condensation at a low rate. Eventually vaporization slows down and condensation occurs faster. Eventually both rates become equal. Equilibrium.

Types of Equilibrium (by phase)

Homogeneous, Heterogeneous

Phase

A homogeneous portion of matter.

Homogeneous Equilibrium

Reactants and products are in the same phase (state), e.g. H2(g) + I2(g) ⇌ 2HI(g).

Heterogeneous Equilibrium

Reactants and products are in different phases, e.g. CaCO3(s) ⇌ CaO(s) + CO2(g).

Graphical Representation of Dynamic Equilibrium

The curves become horizontal as the rate of reaction becomes equal between reactants and products.

Equilibrium Composition

The concentration of reactants and products at equilibrium.

Amounts/Rates at Equilibrium

The amount of each product/concentration does not have to be equal, only the rates of reaction.

Rate of Reaction in Dynamic vs Static Equilibrium

In dynamic equilibrium the rate is never zero, unless for static equilibrium. The rate of reaction stabilizes as the concentration does so.

Characteristics of Dynamic Equilibrium

Can only be obtained in a closed system; macroscopic properties remain constant; changes in temperature, pressure, volume and concentration can change the equilibrium position (catalysts do not); rate of forward reaction equals rate of reverse reaction; concentration is constant for reactants and products.

Closed System

A system that prevents atoms from being added or escaping the reaction.

Macroscopic Properties

Properties you can measure: colour, pH, [C]. They remain constant at equilibrium.

Effect of Catalysts on Equilibrium

Catalysts do not change the equilibrium position.

Le Chatelier's Principle

When a chemical system at equilibrium is stressed, the system works to restore equilibrium.

Stress (Le Chatelier's Principle)

Includes: change in pressure, change in temperature, change in concentration.

Factors in Le Chatelier's Principle

Concentration, Pressure, temperature

Concentration (Le Chatelier's Principle)

When concentration is changed, stress is placed on the equilibrium to shift to the side of lower concentration, causing the concentration of said side to increase until equilibrium is reached.

Pressure (Le Chatelier's Principle)

Pressure only affects reactions involving gases. The more pressure, the more molecules colliding and therefore the more reactants. When pressure is changed, stress is placed on the equilibrium to shift to the side of lower pressure, causing the pressure to increase on said side until equilibrium is reached. If only one side has gas molecules, the equilibrium will always shift to the side with no gas molecules.

Temperature (Le Chatelier’s Principle)

One reaction is exothermic while the other is equally endothermic. When temperature is increased, equilibrium shifts to the side of the products from the endothermic reaction. Vice versa for decreasing temperature.

Effect of Catalyst on Equilibrium

No effect on equilibrium other than decreasing the time taken to reach equilibrium by increasing the rate of reaction throughout