Chemical energetics: Thermochemistry Flashcards
Standard enthalpy change of reaction
Energy change when molar quantities of reactants as stated in the thermochemical equation are reacted together under standard conditions
Standard enthalpy change of neutralisation
Energy evolved when one mole of water is formed from neutralisation of an acid and alkali under standard conditions
Standard enthalpy change of combustion
Energy evolved when one mole of a substance is burnt completely in excess oxygen under standard conditions
Standard enthalpy change of atomisation of elements
Energy absorbed when one mole of gaseous atoms is formed from its element under standard conditions
Standard enthalpy change of atomisation of compounds
Energy absorbed when one mole of a compound is converted into its constituent gaseous atoms under standard conditions
Standard Bond dissociation enthalpy/ Bond energy
Energy required to break one mole of covalent bonds between 2 atoms in the gaseous state under standard conditions
First ionisation energy
The energy absorbed to remove one mole of electrons from one mole of gaseous atoms to form one mole of singly-charged gaseous cations
X (g) -> X+ (g) + e triangleH = 1st I.E.
First electron affinity
The energy change when one mole of electrons is added to one moles of gaseous atoms to form one mole of singly-charged gaseous anions
X (g) + e -> X- (g) +_triangleH = E.A.
Standard lattice energy
Energy evolved when one mole of ionic compound is form from its constituent gaseous ions under standard conditions
Standard enthalpy change of hydration
Energy change when one mole of gaseous ions is surrounded by water molecules, forming a solution at infinite dilution under standard conditions
Standard enthalpy change of solution
Energy change when one mole of substance is dissolved by solvent, such that further dilution does not produce anymore energy change under standard conditions
Standard enthalpy change of formation
Energy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions
Standard conditions :)
- 25 degree celsius/ 298 K
- 1 bar/ 10^5 Pa
- Exists as most stable physical state or allotropic form at standard conditions
- concentration of 1.0moldm^-3
Hess’ Law of constant heat of summation
states that the enthalpy change of a chemical reaction is the same regardless of the rate the reaction takes, provided the reactants and products, initial and final conditions are the same
formulas
^Hrxn = ^Hf of products - ^Hf of reactants
^Hrxn = ^Hc of reactants - ^Hc of products
^Hrxn = energies of bond broken - energies of bond formed
^Hsol = ^Hhyd - L.E
Q = mc^T
^H = Q / n
