Thermochemistry and Calorimetry Lecture Notes

A collection of vocabulary flashcards defining standard enthalpy changes, energy types, and calorimetry concepts from the provided chemistry transcript.

Standard Enthalpy Change of Reaction ($\Delta H_r^{\circ}$)

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

Standard Enthalpy Change of Formation ($\Delta H_f^{\circ}$)

The heat change when one mole of a compound is formed from its constituent elements in their standard physical states at $298\,K$ and $1\,bar$. For elements in their standard state, $\Delta H_f^{\circ} = 0$.

Standard Enthalpy Change of Combustion ($\Delta H_c^{\circ}$)

The heat evolved when one mole of a substance is completely burnt in excess oxygen at $298\,K$ and $1\,bar$. State symbols for water must be liquid.

Standard Enthalpy Change of Neutralisation ($\Delta H_n^{\circ}$)

The heat change when an acid and a base react to form one mole of water at $298\,K$ and $1\,bar$. For a strong acid and strong base, this is usually $-57.3\,kJ\,mol^{-1}$.

Standard Enthalpy Change of Hydration ($\Delta H_{hyd}^{\circ}$)

The heat evolved when one mole of the gaseous ions dissolved in water to form hydrated ions of infinite dilution at $298\,K$ and $1\,bar$. It is always exothermic.

Standard Enthalpy Change of Solution ($\Delta H_{sol}^{\circ}$)

The heat change when one mole of a substance is dissolved in water to form a solution of infinite dilution at $298\,K$ and $1\,bar$. It satisfies the equation: $\Delta H_{sol}^{\circ} = (-\Delta H_{latt}^{\circ}) + \Delta H_{hyd}^{\circ}(\text{cation}) + \Delta H_{hyd}^{\circ}(\text{anion})$.

Standard Enthalpy Change of Atomisation (of an element) ($\Delta H_{atom}^{\circ}$)

The heat absorbed when one mole of gaseous atoms is formed from its element in its standard state at $298\,K$ and $1\,bar$. For gaseous diatomic elements, it equals $\frac{1}{2} \times \text{Bond Energy of } X-X$.

Standard Enthalpy Change of Atomisation (of a compound) ($\Delta H_{atom}^{\circ}$)

The heat absorbed when gaseous atoms are formed from one mole of a compound at $298\,K$ and $1\,bar$. The 'one mole' refers to the compound being atomized.

First ionisation energy ($I.E. (1st)$)

The 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.

First electron affinity ($1st\,E.A.$)

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

Second electron affinity ($2nd\,E.A.$)

The energy required to add an electron to a singly charged negative anion; it is always endothermic because energy is needed to overcome electrostatic repulsion.

Lattice Energy ($L.E.$)

The heat evolved when one mole of the solid ionic compound is formed from its isolated gaseous ions. Its magnitude is proportional to $\frac{q_{+} \times q_{-}}{r_{+} + r_{-}}$.

Bond Energy ($B.E.$)

The energy required to break one mole of covalent bonds between two atoms in a gaseous state. It is always a positive value (endothermic).

Neutralisation of Weak Acid (WA) and Strong Base (SB)

The $\Delta H_n^{\circ}$ is less exothermic than that of SA and SB because energy released during neutralisation is absorbed to complete the dissociation of the weak acid.

Theoretical vs Experimental Lattice Energy

A comparison used to indicate the degree of covalent character in an ionic compound. A significant difference suggests the bonding is not purely ionic.