Octane. C_8H_18. a primai constituent of gasoline, bums in air C_8H_18(C) + 12 1
ID: 1008484 • Letter: O
Question
Octane. C_8H_18. a primai constituent of gasoline, bums in air C_8H_18(C) + 12 1/2 0_2(g) rightarrow 8 CO_2(g) + 9 H_2O(C) A 1.00-g sample of octane is burned in a constant volume calorimeter. The calorimeter is in an insulated container with 1.20 kg of water. The temperance of the water and the bomb rises from 25.00 degree C (298.15 K) to 33.21 degree C (306.36 K). The heat required to raise the bomb's temperature (its heat capacity). C_bomb- is 837 JK. The specific heat of water is 4.184 J/g-K. What is the heat of combustion per gram of octane? What is the heat of combustion per mole of octane? WHAT DO YOU KNOW? There are energy changes for the three components of this system: the energy evolved in the reaction, q^the energy absorbed by the water. q_Water: and the energy absorbed by the calorimeter, q_bomb- You know the following: the molar mass of octane, masses of the sample and the calorimeter water. T_mitia. T_final. Q_bomb. and C_water. You can assume no energy loss to the soundings.Explanation / Answer
heat given off by burning 1 g of octane = heat absorbed by water and bomb
H = -[837 J/K + (1.20x 103 g)(4.181 J/g-K)](306.35 - 298.15K)
H = -4.80x104 J or -48.0 kJ/g octane (exothermic)
(-48.0 kJ/g)(114 g / mol) = -5.47x103 kJ/mol
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