Physical Chemistry

Question 1

How does atomic radius change across a period and down a group?

Answer 1

Atomic radius decreases across a period due to increased nuclear charge pulling electrons closer. It increases down a group due to additional electron shells.

Question 2

How does ionic radius compare to atomic radius for cations and anions

Answer 2

Cations are smaller than their neutral atoms due to electron loss, reducing repulsion. Anions are larger due to electron gain, increasing repulsion.

Question 3

How does ionization energy change across a period and down a group?

Answer 3

Ionization energy increases across a period due to stronger nuclear attraction and decreases down a group due to increased shielding and atomic radius.

Question 4

Cations
(Ammonium, Zinc, Silver)

Answer 4

Ammonium → NH₄⁺
Zinc → Zn²⁺
Silver → Ag⁺

Question 5

Anions (Nitrate, Carbonate, Sulfate, Hydroxide, Bicarbonate, Phosphate)

Answer 5

Nitrate → NO₃⁻
Carbonate → CO₃²⁻
Sulfate → SO₄²⁻
Hydroxide → OH⁻
Bicarbonate → HCO₃⁻
Phosphate → PO₄³⁻

Question 6

What factors influence electronegativity?

Answer 6

Nuclear charge (more protons increase it), atomic radius (smaller atoms have higher electronegativity), and shielding (more shielding reduces it).

Question 7

How does electronegativity change across a period and down a group?

Answer 7

Electronegativity increases across a period due to stronger nuclear attraction and decreases down a group due to increased atomic size and shielding.

Question 8

How is a sigma (σ) bond formed?

Answer 8

By the direct overlap of atomic orbitals between bonding atoms.

Question 9

How is a pi (π) bond formed?

Answer 9

By the sideways overlap of adjacent p orbitals above and below the σ bond.

Question 10

What is hybridization and what are sp, sp², and sp³ orbitals?

Answer 10

Hybridization is the mixing of atomic orbitals.
sp = linear (180°)
sp² = trigonal planar (120°)
sp³ = tetrahedral (109.5°).

Question 11

What is bond energy?

Answer 11

The energy required to break one mole of a particular covalent bond in the gaseous state.

Question 12

What effect does a catalyst have on equilibrium?

Answer 12

A catalyst speeds up both forward and reverse reactions equally but does not change the equilibrium position.

Question 13

Linear

Answer 13

Bonding Pairs: 2 (double bonds)
Bond Angle: 180°

Question 14

Bent/ Non Linear

Answer 14

Bonding Pairs: 2
Lone Pairs: 2
Bond Angle: 104.5°

Question 15

Pyramidal

Answer 15

Bonding Pairs: 3
Lone Pairs: 1
Bond Angle: 107°

Question 16

Trigonal Bipyramidal

Answer 16

Bonding Pairs: 5
Bond Angles: 120° (equatorial), 90° (axial)

Question 17

Tetrahedral

Answer 17

Bonding Pairs: 4
Bond Angle: 109.5°

Question 18

Octahedral

Answer 18

Bonding Pairs: 6
Bond Angle: 90°

Question 19

Trigonal Planar

Answer 19

Bonding Pairs: 3
Bond Angle: 120°

Question 20

What is bond length?

Answer 20

The internuclear distance between two covalently bonded atoms.

Question 21

What is the lattice structure of sodium chloride and magnesium oxide?

Answer 21

Giant ionic lattice where oppositely charged ions form a strong electrostatic network.

Question 22

What is the structure of iodine, buckminsterfullerene (C60), and ice?

Answer 22

Simple molecular structures with weak intermolecular forces.

Question 23

What is the structure of silicon(IV) oxide, graphite, and diamond?

Answer 23

Giant covalent structures with strong covalent bonding.

Graphite has layers with delocalized electrons

Diamond has a tetrahedral network

SiO2 has a 3D lattice.

Question 24

What is the structure of metallic solids like copper?

Answer 24

Giant metallic lattice with delocalized electrons allowing conductivity and malleability.

Question 25

What does it mean if ΔH is negative or positive?

Answer 25

Negative ΔH means an exothermic reaction (heat released). Positive ΔH means an endothermic reaction (heat absorbed).

Question 26

What are standard conditions for enthalpy changes?

Answer 26

298K (25°C) and 101kPa pressure.

Question 27

ΔHf – Enthalpy change of formation

Answer 27

The enthalpy change when one mole of a compound is formed from its elements under standard conditions with all reactants and products in their standard states.

Question 28

ΔHr – Enthalpy change of reaction

Answer 28

The enthalpy change when the reactants react together under standard conditions with all substances in their standard states.

Question 29

ΔHneut – Enthalpy change of neutralization

Answer 29

The enthalpy change when one mole of water is formed by the neutralization of an acid with an alkali under standard conditions

Question 30

ΔHc – Enthalpy change of combustion

Answer 30

The enthalpy change when one mole of a substance is completely burned in excess oxygen under standard conditions with all reactants and products in their standard states.

Question 31

What is the formula for calculating enthalpy change from experimental data?

Answer 31

q = mcΔT where q = heat energy, m = mass, c = specific heat capacity, ΔT = temperature change. ΔH = -q/n where q= heat energy, n= number of moles

Question 32

What is a reversible reaction?

Answer 32

A reaction that can proceed in both forward and reverse directions under suitable conditions.

Question 33

What is dynamic equilibrium?

Answer 33

A state where the rate of the forward reaction equals the rate of the reverse reaction, and concentrations of reactants and products remain constant.

Question 34

What is Le Chatelier’s principle?

Answer 34

If a system at equilibrium is subjected to a change in conditions, the system shifts to counteract the change and restore equilibrium.

Question 35

How do changes in temperature, concentration, and pressure affect equilibrium?

Answer 35

Increasing temperature favors the endothermic direction. Increasing reactant concentration favors the forward reaction. Increasing pressure favors the side with fewer gas molecules.

Question 36

How do temperature, concentration, and pressure changes affect the equilibrium constant (Kc)?

Answer 36

Temperature changes alter Kc, but concentration and pressure do not affect its value.

Question 37

How does temperature affect reaction rate in terms of the Boltzmann distribution?

Answer 37

Higher temperature shifts the peak of the curve to the right, increasing the number of molecules with energy ≥ activation energy (Ea), leading to more effective collisions.

Question 38

How does pressure affect reaction rate?

Answer 38

Higher pressure increases the frequency of collisions, leading to a faster reaction rate.

Question 39

How does the Boltzmann distribution explain the effect of a catalyst?

Answer 39

A catalyst lowers activation energy (Ea), increasing the number of molecules able to react, leading to a higher reaction rate.