How to Figure Out Latent Heat of Fusion

Melting of Ice

• 1

  Suppose a physics problem asks for the amount of heat required to melt 5 lb. ice at its melting temperature.

• 2

  Find the latent heat of fusion of ice (144 BTU per pound) from tables in a chemistry or physics handbook or textbook.

• 3

  Use the equation: Q = ML, where Q is heat, M is mass and L is latent heat of fusion.

  Substitute the required values into the equation and calculate the answer, as follows: 5 lb. x 144 BTU / lb. = 720 BTU.

Solidification of Lead

• 4

  Consider a problem that asks for the amount of heat released during solidification of 10 lb. of liquid lead.

• 5

  Find the latent heat of fusion of lead (9.89 BTU / pound) and substitute the required values into the equation.

• 6

  Calculate the answer as follows: Q = ML = 10 lb. x 9.89 BTU / lb. = 98.9 BTU.

Molar Heat of Fusion

• 7

  Suppose you need to determine the "molar heat of fusion" of an element or compound, such as water (H2O.)

• 8

  Find the molar mass of water from a chemistry handbook or textbook, or determine it by adding together the atomic weights of the atoms in a water molecule, as follows: (2 x 1) + 16 = 18 lb. / pound-mole.

  Note that a mole can be expressed in any weight unit, provided the units used in ensuing calculations are consistent.

• 9

  Determine the molar heat of fusion of water by multiplying the heat of fusion by the molar mass, as follows: 144 BTU / lb. x 18 lb. / pound-mole = 2,592 BTU / pound-mole.