22.4 entropy

general units of entropy

JK^-1mol^-1

general rules for the entropy value of solids, liquids and gases

• solids have the smallest entropies

• liquids have greater entropies

• gases have the greatest entropies

when a substance changes from a solid to a liquid to a gas what happens to its entropy

• it increases

• melting and boiling increase the randomness of the particles

• energy is spread out more and the entropy charge is positive

why do reactions that produce gases result in an increase in entropy

• production of a gas increases the disorder of particles

• energy is more spread out and the change in entropy is positive

standard entropy definition

the entropy of one mole of a substance, under standard condition (100kPa and 298K)

• always have the unit of JK-1mol-1

• are always positive

equation for calculating entropy changes