Energetics

Question 1

Endothermic Reaction

Answer 1

Positive Enthalphy Change
Bond breaking
Heat absorbed from surroundings

Question 2

Exothermic Reaction

Answer 2

Negative Enthalpy Change
Bond forming
Heat released to surroundings

Question 3

Standard Enthalpy Change of Combustion

Answer 3

Energy evolved when one.mole of the substance is completely burnt in oxygen under standard conditions
Hc = Hcom (rxt) - Hcom (pdt)

Question 4

Standard Enthalpy Change of Neutralisation

Answer 4

Energy evolved when one mole of water is formed from the neutralisation between an acid and base under standard conditions

Question 5

What do you assume during a calorimetry experiment?

Answer 5

Negligible heat lost or gained from the surroundings due to insulation

Question 6

Standard Enthalpy Change of Formation

Answer 6

Energy change when one mole of the substance is formed from its constituent elements under standard conditions
Hc = Hf (pdt) - Hf (rxt)

Question 7

Bond energy

Answer 7

Average energy absorbed to break one mole of X-Y covalent bonds in the gaseous state to form gaseous atoms under standard conditions

Question 8

Standard Enthalpy Change of Atomisation

Answer 8

Energy absorbed when one mole of gaseous atoms is formed from the element under standard conditions

Question 9

First Ionisation Energy

Answer 9

Energy absorbed when one mole of gaseous atoms loses one mole of electrons to form one mole of gaseous singly positively charged ions

Question 10

First Electron Affinity

Answer 10

Energy evolved when one mole of gaseous atoms acquires one mole of electrons to form one mole of singly negatively charged gaseous ions

Question 11

Why is the 1st EA always exothermic, the 2nd EA always endothermic?

Answer 11

Exothermic: Energy released when nucleus attracts an electron is larger than energy absorbed to overcome inter-electronic repulsion
Endothermic: Energy must be supplied to overcome repulsive forces between two negatively charged species (since electron is added to negatively charged ion)

Question 12

Lattice Energy

Answer 12

Energy evolved when one mole of solid ionic compound is formed from its constituent gaseous ions under standard conditions
Determined by the formula concerning charge over radius

Question 13

Standard Enthalpy Change of Hydration

Answer 13

Energy evolved when one mole of gaseous ions is hydrated under standard conditions

Question 14

Standard Enthalpy Change of Solution

Answer 14

Energy change when one mole of substance is completely dissolved in a solvent to form an infinitely dilute solution under standard conditions
Hsol = Hhyd - Hlatt

Question 15

Entropy

Answer 15

Degree of disorder of matter and the ways to distribute energy in a reaction