Latent Heat and Relativity
What is the relationship between Latent Heat and E =
Einstein's famous equation states the equivalency of energy and mass. The
"c^2" however, means that a very small loss in mass yields a very large
amount of energy. The energies of chemical reactions and changes of state
involve quantities of energy that are so extremely small compared to the
equivalent change in mass that for all practical purposes the change in mass
can be ignored. Only in nuclear reactions does the energy and mass changes
If you have a perfectly sealed vacuum jar half-full of water,
when 0 degrees C and melted it will weigh slightly more
than when 0 degrees C (same temperature) but frozen.
Likewise 90% ice and 10% water weighs less than 10% ice and 90% water.
To melt ice requires slowly putting in energy.
That energy has mass.
During that time the temperature will remain constant,
the ratio of ice/water will decrease,
and the mass will ever so slightly increase.
Melting 1kg of ice requires 80kcal or (x4.2=) 335 kJoule of energy.
E=mc2: --> m= E/c2 = 335kJ / (3e10meter/sec)^2 = 3.3e5J / 9e20 =
1kg vs. 4e-16 kg.
The mass increases by much less than 1 trillionth.
Good luck imagining how we could even try to measure it.
Click here to return to the Physics Archives
Update: June 2012