What equations must be used to calculate the heat associated with a phase change?

The equations must be used to calculate the heat associated with phase change is,

        Q=m×∆H(vap)

    or Q=m×∆H(fus)

here;

∆H= heat required for one gram of the substance to undergo the phase change.

*If you're going from solid to liquid, you use ∆H-heat of fusion (called the heat of fusion), which represents the heat required for 1 gram of a substance to change from solid to liquid at the melting point.

*If you're going from liquid to gas, you use ∆H-heat of vaporization (called the heat of vaporization), which represents the heat required for 1 gram of the substance to change from liquid to gas at boiling point.

For water, the values are usually given to be

ΔHfus = 334 J/g  and  

ΔHvap=2257 J/g.

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most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).