CHEMISTRY 5070 · STRUCTURED PRACTICE
1
(a)
[2]Define the term enthalpy change, ΔH, of a chemical reaction and state the sign of ΔH for an endothermic process.
(b)
[5]A student dissolves 4.00 g of ammonium nitrate, (M_r = 80.0), in 50.0 cm³ of water in a polystyrene cup. The temperature drops from 21.5 °C to 15.5 °C.
(i)
[2]Calculate the thermal energy absorbed, Q, in joules. (Assume density of water = 1.00 g/cm³, specific heat capacity c = 4.18 J/(g·°C)).
(ii)
[1]Calculate the amount, in moles, of dissolved.
(iii)
[2]Determine the molar enthalpy change of solution, ΔH_sol, in kJ/mol. Include the sign.
(c)
[2]Explain in terms of kinetic particle theory why the temperature of the solution decreases during dissolving.
Total: 9 marks