Definition of various type of standard enthalpy changes, Thermochemistry Flashcards
Definition of standard enthalpy change of reaction
Change in enthalpy when molar quantities of reactants react together at 298K and 1 bar, standard conditions. Exo/Endo
Definition of standard enthalpy change of neutralisation
Enthalpy change when an acid and bas reacts to form 1 mole of water at 298k and 1 bar. Exothermic
Definition of standard enthalpy of combustion
Heat evolved when 1 mole of a substance is completely burnt in excess oxygen at 298k and 1 bar. Always exothermic
Definition of Standard enthalpy change of formation
Change in enthalpy when 1 mole of a compound is formed from its constituent elements in their standard physical states at 298K and 1 bar. Exo/Endo
Define lattice energy
Heat evolved when 1 mole of solid ionic compo
und is formed from its isolated gaseous ions at 298k and 1 bar. Always exo
Pressure, Temperature, and concentration at Standard Conditions
1 bar, 25 degrees, 1 mol/dm-3 (Not the same as standard temperature and pressure (s.t.p) and room temperature and pressure (r.t.p))
What are the factors affecting the strength of Lattice energy
Magnitude of lattice energy is directly proportional to charges on the ions and inversely proportional to the ionic radius. L.E ~ (q+ x q-)/(r+ + r-)
If theoretical value of lattice energy does not agree well with experimental value …
Bonding in compound is purely not ionic but has considerable percentage of covalent character.
If theoretical value of lattice energy agrees well with experimental value …
Compound is ionic with little or no covalent character.
Define bond energy
It is the required energy to break one mole of covalent bonds between 2 atoms in gaseous state.
Bonds broken/ formed energy relation and endo or exo
Bonds formed, energy is absorbed and so endothermic. Bonds broken, energy is released so exothermic.
