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

Moles of acetone in 87.1 grams of acetone=$\dfrac{given\ mass }{molar\ mass}=\dfrac{87.1}{58}=1.5 moles$

Std enthalpy change of fusion of acetone , $ΔH^o_{fus}=5.7 kJ/mol$

Melting point of acetone is -95 ⁰C

Energy change in transition from -154⁰ C to -95 ⁰C = $nC_p\Delta T=1.5*96*59=8496 J$

Energy change in phase change i.e. solid to liquid=$n*\Delta H^0_{fus}=1.5*5.7=8.55 kJ=8550J$

Energy change in transition from -95⁰C to -42⁰C = $nC_p\Delta T=1.5*125.5*53=9977 J$

$Total\ energy\ required = Sum \ of\ all\ the \ above\ energy = 8496+8550+9977 = 27023 J=27.023 kJ$