Question

The melting point of a certain substance is `70^(@)C` and its normal boiling point is `450^(@)C`. Its enthalpy of fusion is `30.0cal//g`, enthalpy of vaporisation is `45.0 cal//g` and its heat capacity is `0.215 cal g^(-1)K^(-1)`. Calculate the heat required to convert `100g` of substance from solid state at `70^(@)C` to vapour state at `450^(@)C`.

Answer 1

`underset(70^(@)C)(Soli d) overset(DeltaH_(1))rarrunderset(70^(@)C)(Liqui d)overset(DeltaH_(2))rarr underset(450^(@)C)(Liqui d) overset(DeltaH_(3))rarr underset(450^(@)C)(Vapour)`
`DeltaH_(Total)=DletaH_(1)+DeltaH_(2)+DeltaH_(3)`
`=30xx100+100xx0.215xx380+45xx100`
`3000+8170+4500`
`=15670cal=15.67kcal`