If the heat of fusion for ethyl alcohol is 26 cal/g, how many grams must freeze to release 780 cal?

26 cal/g x ??g = 780 cal

30

To answer this question, we can use the formula:

Q = m * ΔH

where:
Q is the amount of heat released (in cal),
m is the mass of the substance that freezes (in g), and
ΔH is the heat of fusion (in cal/g).

We are given:
ΔH = 26 cal/g
Q = 780 cal

We need to find the mass, m.

Rearranging the formula gives us:

m = Q / ΔH

Substituting the given values:

m = 780 cal / 26 cal/g

Calculating the value:

m = 30 g

Therefore, 30 grams of ethyl alcohol must freeze to release 780 calories of heat.