Chemistry Equilibrium Explanations

LCP explanation example: Adding Cl2 to the equilibrium system in a reaction of Cl2 + CO →← COCL2

When Cl2 is added to the equilibrium system, the concentration of Cl2 increases. According to LCP, the system shifts to partially counteract the imposed change by favouring the forward reaction to decrease the concentration of Cl2. Thus, equilibrium shifts to the right. This results in the increased concentration of COCl2 and a decreased concentration of both Cl2 and CO.

LCP explanation outline

1. What happens when you change concentration/temperature/catalyst? Eg.

concentration of reactant species increase, two species react (must include reaction)

2. According to LCP, the system shifts to partially counteract the imposed change by

favouring the forward/reverse (endo/exo for temp) reaction to (explain counteracted

change)

3. Thus, equilibrium shifts to the left/right

4. This results in the increased concentration of (name species) and hence (describe

colour change if there is one)

Rate explanation outline

1. What happens when you change concentration/temperature/catalyst? Eg.

concentration of reactant species increase, two species react (must include reaction)

2. How does this affect the rate of both reactions?

3. Thus, forward/reverse reaction is proceeding at a greater rate

4. This results in the increased concentration of (name species) and hence (describe

colour change if there is one

Rate example

When Cl2 is added to the equilibrium system, the concentration of Cl2 increases. This increases the rate of the forward reaction, whilst the rate of the reverse reaction is instantaneously unaffected. Thus the forward reaction is proceeding at a greater rate. This results in the increased concentration of COCl2 and a decreased concentration of both Cl2 and CO.

Collision theory

1. What happens when you change concentration/temperature/catalyst? Eg. concentration of reactant species increase, two species react (must include reaction)

2. How does this affect the frequency of successful collisions (talk about frequency and proportion first)?

3. How does this affect the rate of both reactions?

4. Thus, forward/reverse reaction is proceeding at a greater rate

5. This results in the increased concentration of (name species) and hence (describe colour change if there is one)

Collision theory example

When Cl2 is added to the equilibrium system, the concentration of Cl2 increases. This increases the frequency of collisions between Cl2 and CO, increasing the frequency of successful collisions between the reactants. This increases the rate of the forward reaction, whilst the rate of the reverse reaction is instantaneously unaffected. Thus the forward reaction is proceeding at a greater rate. This results in the increased concentration of COCl2 and a decreased concentration of both Cl2 and CO.

What determines the boiling point of a substance?

The boiling point of a substance is determined by the strength of its intermolecular forces (IMFs). The greater the sum of IMFs, the more heat is required to disrupt these forces, leading to a higher boiling point.

What type of intermolecular forces do alkanes exhibit?

Alkanes are non-polar molecules and therefore only exhibit dispersion forces.

How does molecular mass affect the boiling point of alkanes?

As the molecular mass of alkanes increases, the strength of the dispersion forces also increases, resulting in a higher boiling point.

Which alkane has the highest boiling point among CH4, C2H6, and C3H8?

Propane (C3H8) has the highest boiling point because it has the strongest intermolecular forces due to its greater molecular mass.

How do the boiling points of C2H6, CH2O, and CH3OH compare?

Ethane (C2H6) is non-polar with only dispersion forces leading to the lowest boiling point. Methanal (CH2O) is polar and has dipole-dipole forces in addition to dispersion forces, resulting in a higher boiling point. Methanol (CH3OH) is highly polar and exhibits hydrogen bonding, dipole-dipole forces, and dispersion forces, thus having the highest boiling point.

What is hydrogen bonding and how does it affect boiling points?

Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms (e.g., O, N, F). It significantly increases the boiling point due to the strong attraction between molecules.

What are the steps to explain solubility?

1. State which intermolecular forces are exhibited by the solute and the solvent.

2. Identify the predominant intermolecular force exhibited by the solute and the solvent.

3. State which new intermolecular forces can form between the solute and the solvent.

4. If the substances are soluble, this is because the energy released when new solute-solvent forces form is sufficient to overcome the original solute-solute and solvent-solvent forces, or the strength of the new solute-solvent forces formed are sufficient to overcome the original solute-solute and solvent-solvent forces.

5. If the substances are insoluble, this is because the energy released when new solute-solvent forces form is not sufficient to overcome either the original solute-solute forces or the original solvent-solvent forces, or the strength of the new solute-solvent forces formed are not sufficient to overcome either the original solute-solute forces or the original solvent-solvent forces.

Cations are all neutral except for:

NH4+, Fe3+, Al3+, Cr3+ which are acidic

All anions are basic except for:

HSO4-, H2PO4- which are acidic Cl-, Br-, I-, NO3-, SO42- which are neutral

What are the strong acids listed?

Strong acids include: Hydrochloric acid (HCl), Hydrobromic acid (HBr), Hydroiodic acid (HI), Nitric acid (HNO3), Sulfuric acid (H2SO4), Perchloric acid (HClO4).

What acids are considered weak acids?

Weak acids include: Ethanoic acid (CH3COOH), Hydrofluoric acid (HF), Carbonic acid (H2CO3), Phosphoric acid (H3PO4), Citric acid, and Formic acid (HCOOH).

What is the common shortcut for identifying strong acids?

A common shortcut is: 'Strong acids are the halogen acids (except HF) plus nitric and sulfuric acid.'

What is the key conceptual rule to distinguish strong and weak acids?

Strong vs weak acids are determined by the degree of ionisation, NOT by concentration.

How can you recognize weak acids in organic chemistry?

If you see -COOH in the formula, it is usually a weak carboxylic acid.

Is HBr a strong or weak acid?

HBr (hydrobromic acid) is a strong acid; it fully ionises in water.

What happens when HBr is dissolved in water?

The reaction is: HBr(aq) + H2O(l) → H3O+(aq) + Br−(aq). This means almost every HBr molecule donates its proton.

What pattern can be noted regarding the strength of halogen acids?

As you go down the halogen group, the H–X bond gets weaker, making it easier to ionise, but HF is an exception due to its very strong H–F bond.

Which acid has the exception in the strong acid category?

HF (hydrofluoric acid) is a weak acid despite being a halogen acid; this is due to its very strong H–F bond.