Chemical Energetics

The standard enthalpy change of hydration, ∆Hhyd°

Heat evolved when one mole of the gaseous ions dissolved in water to form hydrated ions of infinite dilution at 298 K and 1 bar. (always exothermic)

1st E.A is ____ while 2nd E.A is ____.

1st E.A is exothermic (forming electrostatic attraction) while 2nd E.A is endothermic (overcome repulsion between incoming 2nd e and negative ion).

Activation energy ,(Ea)

minimum energy which the colliding molecules must possess before a collision will result in a reaction.

The standard enthalpy change of a reaction , ∆Hr°

Heat change when molar quantities of reactants, as stated in the balanced stoichiometric equation, react together at 298 K and 1 bar.

The standard enthalpy change of a combustion, ∆Hc°

Heat evolved when one mole of a substance is completely burnt in excess oxygen at 298 K and 1 bar (always exothermic)

The standard enthalpy change of a neutralisation,∆Hn°

Heat change when an acid and a base react to form one mole of water at 298 K and 1 bar.

Hess' Law states that the

enthalpy change for a chemical reaction is the same regardless of the route the reaction takes, provided the initial states of the reactants and final states of the products are the same.

The standard enthalpy change of formation, ∆Hf°

Heat change when one mole of a compound is formed from its constituent elements in their standard physical states at 298 K and 1 bar.

The bond dissociation energy, B.E

Energy required to break one mole of covalent bonds between two atoms in a gaseous state.(always Endothermic)

Entropy , S∆

measure of the disorder of a system.

The stardard enthalpy change of atomisation, ∆Hatom°

Heat absorbed when one mole of gaseous atoms is formed from its element in its standard state at 298 K and 1 bar.

(always Endothermic)

First ionisation energy

Energy required to remove one mole of the outermost electron from one mole of gaseous atoms of the element to form one mole of gaseous ions with a single positive charge. (always Endothermic)

The first electron affinity, E.A.

Energy evolved when one mole of gaseous atoms accepts one mole of electrons to form one mole of gaseous singly charged negative ions.

Lattice energy, L.E

Heat evolved when one mole of the solid ionic compound is formed from its isolated gaseous ions at 298K and 1 bar. (always exothermic)

The standard enthalpy change of solution, ∆Hsol°

Heat change when one mole of a substance is dissolved in water to form a solution of infinite dilution at 298K and 1 bar.