Witherite is a mineral which is composed mainly of barium carbonate (BaCO 3 ). W

Question

Witherite is a mineral which is composed mainly of barium carbonate (BaCO3). When heated, this compound decomposes to form barium oxide and carbon dioxide, as expressed by the following equation.

BaCO3(s) BaO(s) + CO2(g)

The standard enthalpy change for this reaction is +271.5 kJ/mol, and the standard enthalpies of formation of BaCO3(s) and BaO(s) are given in the table below.

1213.0

548.0

(a) Calculate the standard enthalpy of formation of CO2(g).
kJ/mol

(b) Calculate the standard enthalpy change for the reverse reaction.
kJ/mol

1213.0

548.0

Explanation / Answer

(a) Enthalpy change for the reaction = (Hfo[BaO] +Hfo[CO2] ) - Hfo[BaCO3]

+271.5 = (-548.0 + CO2 ) - (-1213.0)

  Hfo[CO2] = - 393.5 kJ/mol

(b) Reverse reaction

BaO(s) + CO2(g) ---------> BaCO3(s)

Enthalphy change =  Hfo[BaCO3] - ( Hfo[BaO] + Hfo[CO2])

= (-1213.0) - (-548+(-393.5))

= -271.5 kJ/mol

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