A solution calorimeter has a heat capacity of 94.82 J/K. It contains 100.0 mL of

Question

A solution calorimeter has a heat capacity of 94.82 J/K. It contains 100.0 mL of a solution that is 3.0 M in H2SO4 and 0.02500 M in Fe2+. This solution has a heat capacity density of 0.232 J K-1 mL-1. 0.07900g of powdered KMnO4 (FW = 158.034 g/mol) was introduced into the calortimeter giving a resulting Temperature change of + 2.44K. The reaction taking place is:

KMnO4 (s) + 5 Fe 2+ (aq) + 8 H+ (aq) ---> Mn2+ (aq) + 5 Fe 3+ (aq) + K (aq) + 4 H2O (l)

Determine the standard enthalpy of reaction for this reaction.

Explanation / Answer

Heat absorbed by solution = volume x heat capacity density x temperature change

= 100.0 x 0.232 x 2.44 = 56.608 J


Heat absorbed by calorimeter = heat capacity x temperature change

= 94.82 x 2.44 = 231.3608 J


Heat released by reaction = heat absorbed by solution + heat absorbed by calorimeter

= 56.608 + 231.3608 = 287.9688 mol


Moles of KMnO4 = mass/molar mass of KMnO4

= 0.07900/158.034 = 0.000499892 mol


Enthalpy of reaction = -heat released/moles of KMnO4

= -287.9688/0.000499892

= -576062 J/mol = -576 kJ/mol

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