Thermodynamics A2 Flashcards
Define the enthalpy of formation
The standard enthalpy change which occurs when one mole of a compound is produced from its constituent elements in standard conditions of 298k and 100kPa
Define ionisation energy
The standard enthalpy change which occurs when one mole of gaseous atoms become one mole of gaseous ions, producing one mole of electrons
Define enthalpy of atomisation
The standard enthalpy change for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions
Define mean bond enthalpy
The standard enthalpy change which occurs when one mole of gaseous molecules each breaks a covalent bond to from two free radicals, averaged over different compounds
Define electron affinity
The standard enthalpy change which occurs when a mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous ions
Describe the steps for the formation of an ionic compound from its elements
Atomisation of first element, atomisation of second element, ionisation energy of first, electron affinity of the second, formation of lattice energy
Describe the steps for the enthalpy of hydration for an ionic compound
Lattice dissociation enthalpy, hydration enthalpy of first element, hydration enthalpy of second element
Describe the process of hydration
Water molecules cluster around the ions due to its polar sides
Define enthalpy of hydration
The standard enthalpy change which occurs when water molecules surround one mole of gaseous ions
When is a reaction more likely to occur spontaneously
if the final product is more randomly distorted than the reactants
Why are gases more likely to react spontaneously
They are more random than liquids or solids
What is the entropy of a system
The randomness of a system, with the symbol S, given in standard conditions of 298k and 100kPa
What does a positive value for entropy mean
The reaction will occur spontaneously
How to calculate entropy changes of a reaction
Sum of entropy values of products - Sum of entropy values of reactants
What is the Gibbs free energy
∆G = ∆H - T∆S. If ∆G is negative, the reaction is feasible
