Fundamental Concepts in Chemistry and Thermodynamics

Question 1

Why does the H₂O molecule have a bond angle smaller than the ideal tetrahedral angle?

Accepted Answer

Because lone‑pair electron repulsion is stronger than bond‑pair repulsion.

Answer

Because oxygen lacks a d‑subshell for hybridisation.

Answer

Because oxygen's electronegativity is very high.

Answer

Because the O‑H bond is a polar covalent bond.

Question 2

According to molecular orbital theory, why is He₂ not a stable molecule under normal conditions?

Accepted Answer

The number of electrons in bonding and antibonding MOs are equal, giving a bond order of zero.

Answer

Helium is a noble gas and does not form bonds.

Answer

He₂ has a strong paramagnetic character.

Answer

The antibonding MO lies lower in energy than the bonding MO.

Question 3

For the reaction C(s) + O₂(g) → CO₂(g) with ΔH°₍₂₉₈₎ = –393.5 kJ, which statement is correct?

Accepted Answer

It releases heat; the value is the standard enthalpy of formation of CO₂(g).

Answer

It is an exothermic reaction.

Answer

The reaction increases the internal energy of the system.

Answer

The thermal effect depends on excess oxygen.

Question 4

A reaction has ΔH > 0 and ΔS > 0. Under which condition will the reaction be spontaneous?

Accepted Answer

At high temperature (T > ΔH/ΔS).

Answer

Never spontaneous.

Answer

At low temperature (T < ΔH/ΔS).

Answer

At any temperature.

Question 5

For the rate law v = k[A]²[B], what happens to the reaction rate if [A] is doubled while [B] remains constant?

Accepted Answer

The rate increases eightfold.

Answer

The rate does not change.

Answer

The rate doubles.

Answer

The rate quadruples.

Question 6

In the equilibrium PCl₅ ⇌ PCl₃ + Cl₂ at 250 °C with Kc = 0.042, what is the equilibrium concentration of Cl₂ if initial [PCl₅] = 0.10 M and no products are present?

Accepted Answer

0.021 M

Answer

0.084 M

Answer

0.042 M

Answer

0.047 M

Question 7

Which action most effectively raises the boiling point of a solution containing 5 g solute X in 100 g water?

Accepted Answer

Adding more solute X.

Answer

Adding more water.

Answer

Using a container with larger surface area.

Answer

Stirring the solution vigorously.

Question 8

What is the significance of the solubility product (Ksp) for a sparingly soluble salt?

Accepted Answer

It is the product of ion concentrations in a saturated solution at a given temperature.

Answer

It indicates the maximum concentration of the salt in the solvent.

Answer

It always has a value greater than 1.

Answer

It is directly proportional to the solubility of all substances.

Question 9

For a weak electrolyte with degree of ionisation α, how does α change when the solution is diluted (volume increased)?

Accepted Answer

α decreases.

Answer

α remains unchanged.

Answer

α increases.

Answer

α becomes 1 immediately.

Question 10

Which redox couple has the larger standard electrode potential, Fe³⁺/Fe²⁺ (0.77 V) or I₂/I⁻ (0.54 V), and what is the resulting cell potential when they are combined?

Accepted Answer

Fe³⁺ oxidises I⁻; E°cell = 1.31 V.

Answer

Fe³⁺ oxidises I⁻; E°cell = 0.23 V.

Answer

No spontaneous reaction occurs under standard conditions.

Answer

I₂ oxidises Fe²⁺; E°cell = 0.23 V.

Fundamental Concepts in Chemistry and Thermodynamics

Why does the H₂O molecule have a bond angle smaller than the ideal tetrahedral angle?

According to molecular orbital theory, why is He₂ not a stable molecule under normal conditions?

For the reaction C(s) + O₂(g) → CO₂(g) with ΔH°₍₂₉₈₎ = –393.5 kJ, which statement is correct?

A reaction has ΔH > 0 and ΔS > 0. Under which condition will the reaction be spontaneous?

For the rate law v = k[A]²[B], what happens to the reaction rate if [A] is doubled while [B] remains constant?

In the equilibrium PCl₅ ⇌ PCl₃ + Cl₂ at 250 °C with Kc = 0.042, what is the equilibrium concentration of Cl₂ if initial [PCl₅] = 0.10 M and no products are present?

Which action most effectively raises the boiling point of a solution containing 5 g solute X in 100 g water?

What is the significance of the solubility product (Ksp) for a sparingly soluble salt?

For a weak electrolyte with degree of ionisation α, how does α change when the solution is diluted (volume increased)?

Which redox couple has the larger standard electrode potential, Fe³⁺/Fe²⁺ (0.77 V) or I₂/I⁻ (0.54 V), and what is the resulting cell potential when they are combined?

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For the reaction C(s) + O₂(g) → CO₂(g) with ΔH°₍₂₉₈₎ = –393.5 kJ, which statement is correct?

In the equilibrium PCl₅ ⇌ PCl₃ + Cl₂ at 250 °C with Kc = 0.042, what is the equilibrium concentration of Cl₂ if initial [PCl₅] = 0.10 M and no products are present?

Which action most effectively raises the boiling point of a solution containing 5 g solute X in 100 g water?

Which redox couple has the larger standard electrode potential, Fe³⁺/Fe²⁺ (0.77 V) or I₂/I⁻ (0.54 V), and what is the resulting cell potential when they are combined?

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