A2 Paper 1 Definitions (M3 & M5)

Question 1

What is Periodicity?

Answer 1

The repeating trends in physical and chemical properties

Elements are arranged by increasing atomic (proton) number and in groups with similar chemical properties.

Question 2

Why is Mg classed as a s-block element?

Answer 2

S-block element has its highest energy electron in a s subshell

This classification helps in understanding the electron configuration of elements.

Question 3

What is First Ionisation Energy?

Answer 3

The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 4

What is Second Ionisation Energy?

Answer 4

The energy required to remove one electron from each 1+ ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 5

Define Successive Ionisation Energy.

Answer 5

A measure of the energy required to remove each electron in turn

Question 6

Define Metallic Bonding.

Answer 6

Strong electrostatic attraction between positively charged ions (cations) and delocalised electrons

Question 7

What is Disproportionation?

Answer 7

The simultaneous oxidation and reduction of the same element in the same redox reaction

Question 8

Define an Exothermic Reaction.

Answer 8

A reaction where heat energy is released to the surroundings (ΔH is negative)

Question 9

What is an Endothermic Reaction?

Answer 9

A reaction where heat energy is absorbed from the surroundings (ΔH is positive)

Question 10

What is average bond enthalpy, Δ_EH^ϑ?

Answer 10

The average enthalpy change for the breaking of 1 mole of bonds in gaseous molecules.

Question 11

What are standard conditions?

Answer 11

Temperature = 25°C (298K), Pressure = 1 atm (100 kPa), and all solutions must have a concentration = 1.00 mol dm^-3.

Question 12

What is the standard enthalpy change of formation, Δ_fH^ϑ?

Answer 12

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

Question 13

What is the standard enthalpy change of combustion, Δ_cH^ϑ?

Answer 13

The enthalpy change for complete combustion of one mole of a substance under standard conditions, all reactants and products being in their standard states.

Question 14

What is the standard enthalpy change of neutralisation, Δ_neutH^ϑ?

Answer 14

The enthalpy change that accompanies the formation of one mole of H₂O(l) from neutralisation, under standard conditions.

Question 15

What is the rate of reaction?

Answer 15

The change in concentration of a reactant or a product per unit time.

Rate = Concentration of reactant (or product) mol dm^-3; UNITS = mol dm^-3 s^-1

Question 16

What is activation energy?

Answer 16

The minimum energy required to start a reaction by breaking bonds.

Question 17

What is homogeneous catalysis?

Answer 17

Catalysis of a reaction in which the catalyst and the reactants are in the same physical state.

Question 18

What is heterogeneous catalysis?

Answer 18

Catalysis of a reaction in which the catalyst has a different physical state from the reactants.

Question 19

What is dynamic equilibrium?

Answer 19

• Exists in a closed system
• when the rate of the forward reaction is equal to the rate of the reverse reaction
• and the concentrations of reactants and products do not change.

Question 20

What is Le Chatelier’s principle?

Answer 20

When a system in dynamic equilibrium is subjected to change, the equilibrium position will shift to minimise the change.

Question 21

What is the Kc expression for the reaction H₂ + I₂ ↔ 2HI?

Answer 21

Kc = [HI]² / [H₂] [I₂]

Question 22

What is Rate-determining step?

Answer 22

The slowest step in a multi-step reaction

.

Question 23

What is half-life of a reactant, t_1/2?

Answer 23

Time taken for the concentration of the reactant to reduce by half

Question 24

What is the arrhenius equation (in the equation of a straight line form)?

Answer 24

Question 25

What is **Mole fraction x(A)?**

Answer 25

Number of moles of A / total number of moles in a gas mixture

Question 26

Define **Partial Pressure p(A).**

Answer 26

Mole fraction of A x total pressure P

Question 27

What does **enthalpy change of atomisation, Δ_atH^ϑ** represent?

Answer 27

The enthalpy change when one mole of gaseous atoms is formed from its element, under standard conditions

Question 28

Define **first electron affinity, Δ_EA1H^ϑ.**

Answer 28

The enthalpy change when one electron is added to each atom in one mole of gaseous atoms, to form one mole of gaseous 1- ions

Question 29

What is **second electron affinity, Δ_EA2H^ϑ?**

Answer 29

The enthalpy change when one electron is added to each ion in one mole of gaseous 1- ions, to form one mole of gaseous 2- ions

Question 30

Define **Lattice Enthalpy, Δ_LEH^ϑ.**

Answer 30

Enthalpy change when one mole of an ionic compound is formed from its gaseous ions

Question 31

What is **Standard Enthalpy Change of Solution, Δ_solH^ϑ**

Answer 31

Enthalpy change that takes place when one mole of compound (solute) is completely dissolved in water under standard conditions

Question 32

What is **Standard Enthalpy Change of Hydration, Δ_hydH^ϑ?**

Answer 32

The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions ## Footnote This process is critical in understanding ion solvation.

Question 33

What does **Entropy, S** measure?

Answer 33

A measure of the dispersal of energy in a system, greater when the system is more disordered

Question 34

What is **standard entropy change of reaction, ΔS^ϑ?**

Answer 34

The entropy change that accompanies a reaction in molar quantities expressed in a chemical equation under standard conditions

Question 35

What is **Gibbs’ Equation?**

Answer 35

ΔG = ΔH – TΔS

Question 36

When is a reaction classed as being **feasible according to Gibbs’ Equation?**

Answer 36

When ΔG is negative

Question 37

What is a **BrØnsted-Lowry Acid?**

Answer 37

A proton (H⁺) donor

Question 38

Define **BrØnsted-Lowry Base.**

Answer 38

A proton (H⁺) acceptor

Question 39

What is a **Strong Acid?**

Answer 39

Completely dissociates into its ions in solution to donate a proton

Question 40

What is a **Weak Acid?**

Answer 40

Partially dissociates into its ions in solution to donate a proton

Question 41

What is a **salt?**

Answer 41

Is produced when a H⁺ ion from an acid is replaced by a metal ion or an ammonium ion (NH₄)

Question 42

Define the term **conjugate acid-base pair.**

Answer 42

A pair of two species that transform into each other by the gain or loss of a proton (H⁺)

Question 43

What is the **formula for pH?**

Answer 43

pH = -log[H⁺]

Question 44

How to **calculate H⁺?**

Answer 44

H+ = 10^-pH

Question 45

Calculate **pKa.**

Answer 45

pKa = -log[Ka]

Question 46

Calculate **Ka.**

Answer 46

Ka = 10^-pKa

Question 47

Calculate **Kw.**

Answer 47

[H+][OH-]

Question 48

What is a **Buffer Solution?**

Answer 48

A mixture that minimises pH change on addition of small amounts of acid or base

Question 49

What does **standard electrode (redox) potential, Eθ** measure?

Answer 49

The e.m.f. of a half-cell compared with a standard hydrogen half-cell, measured at 298K with solution concentrations of 1 mol dm^-3

Question 50

What is a **Transition Element**.

Answer 50

A d-block element that forms an ion with an incomplete d sub-shell

Question 51

What is a **complex ion?**

Answer 51

A transition metal ion bonded to one or more ligands by coordinate bonds

Question 52

Define **Ligand.**

Answer 52

A molecule or ion that can donate a pair of electrons to the transition metal ion to form a coordinate bond

Question 53

What is a **coordinate bond?**

Answer 53

Shared pair of electrons in which one of the bonded atoms provides both electrons for the shared pair

Question 54

What is **coordination number?**

Answer 54

The total number of coordinate bonds formed between a central metal ion and its ligands

Question 55

Define **monodentate ligand.**

Answer 55

A molecule or ion that can donate one pair of electrons to the transition metal ion to form one coordinate bond. Examples:

Question 56

What is a **bidentate ligand?**

Answer 56

Donates two lone pairs of electrons to the central metal ion to form two coordinate bonds. Examples:

Question 57

What is a **multidentate ligand?**

Answer 57

Donates more than one lone pair of electrons to the central metal ion to form more than one coordinate bond.

Question 58

What is an **optical isomer.**

Answer 58

Stereoisomers that are a pair of non-superimposable mirror images of each other.