Question

A 1.00g sample of octane (C8H18) is burned in a calorimeter that contains 1.20kg of water. The temperature of the water and the bomb rises from 25.00oC to 33.20oC. If the heat capacity of the bomb, Cbomb, is 837J/K calculate the heat given off per mole of octane. Specific heat for water: 4.184 J/g.°C

Please show work, correct equation to use and values. I know how to calculate heat but not sure how to correctly find heat per mole.

86 kJ/mol; 41.2 kJ/mol; 5.48 x 103 kJ/mol; 48.0 kJ/mol; 4.21 kJ/mol

Answer 1

Heat released by combustion of octane = heat gained by water + heat gained by calorimeter

Heat gained by calorimeter = C(cal) * ∆T

= 837*(33.20-25)

= 6863.4 joule or 6.863 KJ

Heat gained by water

= Mass * specific heat * ∆T

= ( 1.20*10^3)*4.184*(33.2 -25)

= 41170.56 joule or 41.171 KJ

Total heat = 41.171 + 6.863

= 48.034 KJ

Moles of octane = mass / molar mass

= 1/ 114

= 8.772*10^-3

8.772*10^-3 mole produces = 48.034 KJ

1 mole will produce = 48.034 / (8.772*10^-3)

= 5.475 *10^3 kJ / mol

Option C

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