Enthalpy and entropy Flashcards
What is the electron affinity?
Enthalpy change when 1 atom in 1 mole of gaseous atoms gain 1 electron to form 1 mole of gaseous 1- ions
What is the enthalpy of atomisation?
1 mole of gaseous atoms from element in its standard state
What is the hydration enthalpy?
1 mole of gaseous ions hydrated fully in water.
What is the enthalpy of solution?
1 mole of ionic solid dissolves in excess water so ions are well separated and do not interact.
What is the bond dissociation enthalpy?
1 mole of covalent bonds are broken in the gaseous form.
What is the lattice enthalpy?
1 mole of solid ionic compound formed from its constituent ions as gaseous.
What is the enthalpy of vapourisation?
1 mole of liquid is turned into a gas.
What is the enthalpy of fusion?
1 mole of solid becomes a liquid.
What is enthalpy?
A measure of the heat constant of a substance.
What are factors affecting ionic compounds enthalpy values?
Greater charge = greater attraction, increasing lattice enthalpy.
Mp - higher lattice enthalpy, higher mp of ionic compound
Solubility - of ionic compounds, affected by relative values of lattice and hydration enthalpies.
Smaller ions have greater attraction because of higher charge density - greater lattice enthalpies and mp due to extra energy/separate oppositely charged ions.
What is entropy?
Disorder - the more disordered something is, the greater the entropy. There is a tendency for entropy to increase.
The more positive the entropy, the more favourable the reaction is.
What is the 3rd law of thermodynamics?
The entropy of a substance is zero at absolute zero and increases with temperature.
The higher the temp, the faster the particles vibrate.
How does entropy affect feasibility?
Reactions are feasible if entropy is increasing.
But the reaction may not happen if the activation energy is too high.
How are entropy changes calculated?
/\S = Sum(products) - sum(reactants)
Where entropy increases, /\S is positive.
What is Gibbs free energy change?
/\G = /\H - T/\S
A decrease in enthalpy is more favourable in a reaction (exothermic).
IF /\G IS LESS THAN/= 0, REACTION IS FEASIBLE.
