Topic 5: Energetics Flashcards
Define the standard enthalpy of combustion.
The enthalpy change for the complete combustion of one mole of a substance in its standard state in excess oxygen under standard conditions. ∆H = kJmol-1. EXOTHERMIC.
Define the standard enthalpy change of reaction.
The enthalpy change when the reactants in a stoichiometric equation react, under standard conditions, to form the products. ΔHr.
Define the standard enthalpy neutralisation.
The enthalpy change when one mole of water is formed by the reaction of an acid with alkali under standard conditions. ΔHneutral. EXOTHERMIC.
Define Hess’s law.
The enthalpy change for any chemical reaction is independent of the route providing the starting conditions and the final conditions (and reactants and products) are the same.
What are the conditions for standard enthalpy changes?
Temperature = 298 K
Pressure = 100 kPa
1 mol dm-3 solutions
Define the bond enthalpy.
The energy needed to break one mole of bonds in gaseous molecules under standard conditions.
Define the enthalpy of formation.
The enthalpy change when one mole of product is formed from its constituent elements in their standard states.
Define the enthalpy ionisation energy.
The standard enthalpy change that occurs on the removal of 1 mole of electrons from 1 mole of gaseous atoms or positively charged ions. ENDOTHERMIC.
Define first electron affinity.
The energy change when 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous ions under standard conditions. EXOTHERMIC.
Define lattice enthalpy.
The enthalpy change that occurs when one mole of a solid ionic compound is separated into gaseous ions under standard conditions (i.e. lattice to ions). ENDOTHERMIC.
Define enthalpy of atomisation/sublimation.
The enthalpy change that occurs when one mole of gaseous atoms is formed from the element in its standard state (i.e. standard state to gas). ENDOTHERMIC.
Define enthalpy of solution.
The enthalpy change when 1 mole of a solute dissolves in sufficient water to form an infinitely dilute solution.*Two steps - lattice enthalpy and enthalpy of hydration.
Define enthalpy of hydration.
The enthalpy change when one mole of gaseous ions is dissolved to form an infinitely dilute solution of one mole of aqueous ions (i.e. ions from gas to aqueous). EXOTHERMIC.
Define enthalpy of dissociation.
The amount of energy required to break a chemical bond between two species.
Define entropy.
The distribution of available energy among the particles. *Measure of disorder. Ordered states (eg. solids) have low entropy, disordered states (eg. gases) have high entropy.
