Chemical Equilibria & Redox Reactions – Lecture Review

These flashcards cover all essential definitions, rules, and principles related to chemical equilibrium and redox reactions from the lecture notes.

What is a reversible reaction?

A reaction in which the products can react together to reform the original reactants.

Give the example of a reversible reaction cited in the notes.

A + B ⇌ C + D

What is dynamic equilibrium?

A state where the forward and reverse reactions occur at the same rate and the concentrations of reactants and products remain constant in a closed system.

List the three conditions required for dynamic equilibrium.

1) Closed system; 2) Constant temperature (and pressure if gases are involved); 3) The reaction must be reversible.

State Le Chatelier’s Principle.

If a change is made to a system at equilibrium, the position of equilibrium shifts to oppose that change.

How does increasing the concentration of reactants affect the equilibrium position?

It shifts the equilibrium to the right, producing more products.

How does increasing the concentration of products affect equilibrium?

It shifts the equilibrium to the left, using up the added products.

How does decreasing the concentration of reactants affect equilibrium?

It shifts the equilibrium to the left.

How does decreasing the concentration of products affect equilibrium?

It shifts the equilibrium to the right.

For gaseous systems, what happens to equilibrium if pressure is increased?

The equilibrium shifts toward the side with fewer moles of gas.

For gaseous systems, what happens if pressure is decreased?

The equilibrium shifts toward the side with more moles of gas.

When will a pressure change NOT affect the equilibrium position of a gaseous reaction?

When the number of moles of gas is the same on both sides of the balanced equation.

How does increasing temperature affect the position of equilibrium?

It shifts in the endothermic direction.

How does decreasing temperature affect the position of equilibrium?

It shifts in the exothermic direction.

What effect does a catalyst have on equilibrium position?

None; it speeds up both the forward and reverse reactions equally, so the position of equilibrium is unchanged.

Write the general expression for the equilibrium constant Kc.

Kc = [products]^n / [reactants]^m (concentrations in mol dm⁻³, powers from the balanced equation).

What does Kc ≫ 1 indicate?

The equilibrium lies far to the right; products are greatly favoured.

What does Kc ≪ 1 indicate?

The equilibrium lies far to the left; reactants are greatly favoured.

What does Kc ≈ 1 indicate?

Comparable amounts of reactants and products are present at equilibrium.

What does the term ‘redox’ mean?

It describes reactions that involve both reduction and oxidation (electron transfer).

Define oxidation in terms of electrons and oxidation number.

Oxidation is the loss of electrons and corresponds to an increase in oxidation number (and, classically, gain of oxygen).

Define reduction in terms of electrons and oxidation number.

Reduction is the gain of electrons and corresponds to a decrease in oxidation number (and, classically, loss of oxygen).

What is an oxidising agent?

A substance that accepts electrons, gets reduced itself, and causes another species to be oxidised.

What is a reducing agent?

A substance that donates electrons, gets oxidised itself, and causes another species to be reduced.

What is an oxidation number?

The charge an atom would have if the compound were fully ionic, used to track oxidation and reduction.

What is the oxidation number of any element in its standard state (e.g., O₂, Cl₂)?

0

What is the oxidation number of a simple ion (e.g., Na⁺, Cl⁻)?

Equal to the charge on the ion.

State the usual oxidation numbers for Group 1 and Group 2 metals.

Group 1: +1; Group 2: +2

What is the usual oxidation number of hydrogen and its common exception?

+1, except –1 in metal hydrides.

What is the usual oxidation number of oxygen and its two key exceptions?

−2 normally; −1 in peroxides and +2 in OF₂.

What is the oxidation number of fluorine in compounds?

Always −1.

What is the sum of oxidation numbers in a neutral compound?

0

What is the sum of oxidation numbers in a polyatomic ion?

It equals the overall charge on the ion.

How can you recognise a redox reaction using oxidation numbers?

Look for species whose oxidation numbers increase (oxidation) and decrease (reduction).

Outline the five steps for writing a redox half-equation.

1) Write the oxidation or reduction change; 2) Balance all atoms except H and O; 3) Balance O with H₂O; 4) Balance H with H⁺; 5) Balance charge with e⁻.

How do you combine two half-equations into a full redox equation?

Multiply each half-equation so electrons cancel, add them together, and simplify if necessary.

Give the summary of key points covered about equilibrium and redox.

Reversible reactions reach dynamic equilibrium, whose position depends on temperature, pressure, and concentration and follows Le Chatelier’s Principle; redox reactions involve electron transfer tracked via oxidation numbers, and half-equations reveal individual oxidation and reduction steps.