Question

How much energy is required to heat 87.1 g acetone (molar mass=58.08 g/mol) from a solid at -154.0°C to a liquid at -42.0°C? The following physical data may be useful.

Answer 1

Heating from -154.0 C to melting point (-95 C) (solid state):

$Q1 = C*n*(t2-t1)=96 J/(mol*K)*10^-3kg/(0.058kg/mol)*(-95+154)K=8.5*10^3J$

Melting:

$Q2=ΔfusH∗h=5.72∗10 ^3 J/mol∗1.5mol=8.6∗10 ^3 J$

Heating from -95 C to -42 C (liquid state):

$Q3=C∗n∗(t3−t2)=126.6J/(mol∗K)∗10 ^ − 3kg/(0.058kg/mol)∗(−42+95)K=10.1∗10 ^ 3 J$

The answer:

$Qsum=Q1+Q2+Q3=8.5∗10 ^3 J+8.6∗10 ^ 3 J+10.1∗10 ^ 3 J=2.7∗10 ^ 4 J$