For copper, with a heat of fusion of 209 J/g, what will be the energy (in joules) absorbed or released when 3.0 moles of liquid copper freezes into a solid.

Answer 1

First, when liquid copper changes from liquid to solid, energy will be liberated or released to the surroundings as it is an exothermic process. So, the answer will have a negative sign.

q = m∆H_fusion

q = heat = ?

m = mass = 3.0 moles Cu x 63.55 g/mol = 190.65 g (converted to grams to be consistent with units for ∆H_f)

∆H_f = 209 J/g

q = (190.65 g)(209 J/g) = 39,846 Joules

Rounding to 2 significant figures (based on 3.0 mol) and designating it as exothermic, we have an answer of....

-40,000 joules