Entropy

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.