A bomb calorimeter is used to determine the amount of energy liberated when a sa

Question

A bomb calorimeter is used to determine the amount of energy liberated when a sample of butane is combusted. The bomb calorimeter is calibrated by combusting 7.62 g of methane (CH_4, MW=16.0g/mol, Delta E_comt, = -902 kJ/mol) which leads to a temperature change of 40.2degree C. After the calibration of the bomb you load 3.40 g of butane into the same calibrated calorimeter and perform your combustion experiment. During this experiment, there is a recorded increase of temperature of 15.7degree C. What is the Delta E of combustion for butane (MW = 58.1 g/mol). Please report your answer to the correct number of significant figures.

Explanation / Answer

Combustion of butane

2C4H10 + 13O2 ---> 8CO2 + 10H2O

dHrxn = 3.40 x 1.67 x 15.7 = -89.1446 J

dHrxn (per mole of butane) = 89.1446 x 58.12/3.40 = -1523.906 J/mol

dErxn = dH - dnRT

           = -1523.906 - 3 x 8.314 x (15.7 + 273)

           = -8.725 kJ/mol

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