Entropy: The greater the entropy, the greater the disorder. Units of entropy are JK-1mol-1
. 0K =
no energy so minimum disorder.
States of Matter: Generally changing from solids -> liquids -> gas by melting and boiling,
increases entropy increase in disorder, more random molecules and ∆S entropy change is
positive. Or forming gas, increases entropy.
Aqueous (NOT LIQUID SINCE (aq)) particles are more disordered than solid (particles).
Change in Number of Gaseous Molecules: Count number of moles. If there is a decrease in
number of gas molecules, decrease in randomness of particles, entropy decreases. Entropy
change is negative. Quote number of gas molecules as well.
Try and recognise when these questions come up- e.g. if presented with equation or asks why
entropy changes.
Standard Entropies: Standard entropy SӨ
is the entropy of one mole of substance, under
standard conditions (100 kPa and 298 K). In data books. Have units of JK-1mol-1. Standard
entropies always positive.
Calculating Entropy Changes: Standard entropies of products and reactants used to calculate
entropy change of reaction. ∆S
Ө = products – reactants. Work out products and reactants
separately and then subtract. Multiply the balancing number with individual standard entropy.
If asked to work out standard entropy of one the products or reactants but given overall
standard entropy change, rearrange equation.