enthalpy and entropy Flashcards
activation energy
the minimum energy required for a reaction to take place
standard conditions
100kpa 298k
Average bond enthalpy equation
Reactant-product
Q=
Mct
Delta h=
-Q/mol
Enthalpy change of formation
Change in enthalpy when one mol of a substance in the standard state is formed from its pure elements under the same conditions. Generally exothermic
Enthalpy change of combustion
Enthalpy change when one mol of a substance is combusted completely in oxygen under standard conditions all reac and prod in their standard state. Generally exothermic.
Enthalpy change of neutralisation
enthalpy change when solutions of an aqeous acid is neutralised by an aqueous base to form one mole of water under standard conditions. Generally exothermic
Enthalpy unit
Kjmol-1
Entropy unit
JK-1 mol-1
Entropy
Measure of dispersal of energy in a system the more disordered a system the higher the entropy
Entropy change equation
Products-reactants
Gibbs equation
DG=DH-TDS
What does Dg need to be for reaction to be feasible
Negative
First ionisation energy
The enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form uni positive ions. Generally endothermic.
Second ionisation energy
The energy change when one mole of electrons is removed from one mole of 1+ gaseous ions to form one mol of 2+ ions. Generally endothermic
First electron affinity
Enthalpy change when one mole of gaseous atoms gain one mole of electrons to form uni negative ions. Generally exothermic
Second electron affinity
The enthalpy change when one mole of 1- gaseous ions gains one mole of electrons to form one mole of 2- ions. Generally endothermic
Lattice energy
the energy change when one mole of an ionic lattice is formed from its gaseous ions under standard conditions. Can be exothermic or endothermic
Enthalpy of atomisation
The enthalpy change when one mole of gaseous atoms is formed from its element in its standard state. Endothermic
Bond enthalpy
The enthalpy change when one mole of gaseous covalent bonds is broken to form gaseous atoms. Endothermic
Enthalpy of hydration
The enthalpy change when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard state. Exothermic
Enthalpy of solution
The enthalpy change when one mole of a compound is completely dissolved in water under standard conditions. Can be exothermic or endothermic
Why would a thermodynamically feasible (dG<0) reaction not occur
it might be thermodynamically feasible but not kinetically feasible as the rate of reaction might be too slow or the activation energy too high
Why might average bond enthalpy differ from actual bond enthalpy?
It is an average of the same bond in a range of compounds with different atoms around it that might affect bond strength
Difference between solution and hydration Enthalpy
Hydration is of ions in gaseous state but solution is compounds in standard state
Difference between bond Enthalpy and atomisation enthalpy
Bond Enthalpy is a mole of bonds from gaseous state but atomisation is mole of element in standard state to gas
