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10 February, 22:10

A 0.1326 g sample of magnesium was burned in an oxygen bomb calorimeter. the total heat capacity of the calorimeter plus water was 5,760 j/°c. if the temperature rise of the calorimeter with water was 0.570°c, calculate the enthalpy of combustion of magnesium. mg (s) + 1/2o2 (g) →mgo (s)

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  1. 10 February, 22:25
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    The enthalpy of combustion of magnesium is - 601.3 kj/mol

    calculation

    ΔH = cΔT

    C (heat capacity) = 5,760 j/°c

    ΔT = 0.570°c

    ΔH = 5760 j/°c x 0.570 °c = 3283.2 j

    convert 3283.2 j into Kj

    1 kj = 1000 j

    kj? = 3283.2 j

    by cross multiplication

    ={ (3283.2 j x 1 kj) / 1000 j} = 3.2832 kj

    Find the moles of Mg

    moles = mass: molar mass

    from periodic table the molar mass of Mg = 24.3 g/mol

    = 0.1326 g: 24.3 g/mol = 0.00546 moles

    find ΔH in KJ/mol

    = 3.2832 kj / 0.00546 moles = 601.3 Kj/mol

    since heat is released during combustion the ΔH is = - 601.3 kj/mol
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