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)

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