Core
Energetics: Enthalpy
Slide 16 of 34
Heating curve
When a solid at below it’s
melting point is heated, heat energy is converted to kinetic
energy as the particles in the solid vibrate more more strongly.
But, when sufficient heat
energy has been added to arrive at (t1) the melting point
of the solid, further heat energy added converts into potential energy as
the particles go from vibrating to flowing, the solid structure breaks down and
it converts into liquid.
Thus, heat energy at the
melting point, converts into potential energy in the liquid
until all the solid has melted (by t2).
Continual heating increases
the kinetic energy of the particles in the liquid, until the
boiling point of the liquid is reached (at t3).
From t3 to t4 the liquid starts evaporating.
That is, the heat energy
added at constant temperature here changes into potential energy of
the particles allowing them to leave the surface of the liquid
and bringing them farther apart.
Continual heating of course
increases the kinetic energy of the gaseous particles.