Core
Energetics: Enthalpy
Slide 14 of 34
Enthalpy change terms for physical changes
For a given substance, total energy (kinetic and
potential) of liquid is greater than that of solid.
In
other words, liquid bromine at 25°C has more kinetic and potential energy than
solide bromine at -7°C (freezing point of
bromine).
Not
only are the molecules in iquid bromine moving faster on average, they are also
farther apart.
At
-7°C, however, liquid and
solid bromine have the same kinetic energy, but liquid
bromine has more potential energy.
At
-7°C the average motion
of the particles is equal but the average distance between
molecules in liquid is greater than in the solid.
Similarly, total energy of gas is greater than that of
liquid.
Steam
at 110° has more
kinetic and potential energy than water at 25°C.
At
100°C however, steam
and water possess equal kinetic energy, but steam has
more potential energy.
And
again, thats why steam at 100°C scalds you more badly than boiling water at
the same temperature.