A 0.1375-g sample of solid magnesium is burned in

aconstant-volume bomb calorimeter that has a heat capacity of

3,024J/oC. The temperature incresases by

1.126oC. Calculate the heat given off by the burning Mg,

in KJ/g and inKJ/mol.

a) Q = 0.025 KJ/g

b) Q = 0.602 KJ/mol

Explanation:

ΔU = Q + W ... first law

∴ a constant volume: ΔV = 0

⇒ W = 0

⇒ ΔU = Q = CvΔT

∴ Cv = 3.024 J/°C

∴ ΔT = 1.126 °C

⇒ Q = (3.024 J/°C) * (1.126 °C) = 3.405 J

⇒ Q = 3.405 E-3 KJ

a) Q [=] KJ/g

⇒ Q = (3.405 E-3 KJ) / (0.1375 g) = 0.025 KJ/g

b) Q [=] KJ/mol

∴ Mw Mg = 24.305 g/mol

⇒ Q = (0.025 KJ/g) * (24.305 g/mol) = 0.602 KJ/mol