One mole of a solid compound Y is warmed from its melting point until it has…

CHEMISTRY · Multi-part · A Level · Chemistry · Energetics · Energetics

Problem

One mole of a solid compound Y is warmed from its melting point until it has completely melted (

\Delta H_{\text{fus}} = 15\,\text{kJ}\,\text{mol}^{-1}

) and then partially decomposes according to

Y(l) \to A(g) + B(g)

with

\Delta H_{\text{rxn}} = -250\,\text{kJ}\,\text{mol}^{-1}

. The total heat released to the surroundings during the experiment is

185\,\text{kJ}

. Assume no other energy changes occur. (a) Calculate the number of moles of

Y

that decomposed. (b) State whether melting is a physical change or a chemical change.