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21 November, 07:04

4. a) The enthalpy change of combustion of hexane was measured using a calorimeter containing 200 cm3 of water; 0.5g of hexane (C6H14) was burnt. The temperature of the water increased by 30 K.

Calculate the enthalpy change of combustion of hexane.

(c=4.18 Jg - 1K-1).

Give your answer in kJ mol-1.

I got - 24794kjmol-1 as combustion for hexane. Do you need to do anything else for the question?

bond values (from previous question):

c-c 347

c-h 413

c=o 805

o-h 464

+1
Answers (1)
  1. 21 November, 07:50
    0
    The heat of combustion of hexane is - 4324kjmol-1

    Explanation:

    Heat of combustion is the heat evolved when a mole of a substance is burned completely in oxygen under standard conditions.

    To solve this problem, all the required values have been given.

    Change in temperature ΔT = 30K

    Mass of water = 200cm3 = 200g

    Mass of Hexane burned = 0.5g

    Step 1:

    Find the amount of hear given off

    Heat evolved = mass * specific eat capacity of water * temperature change

    = 200 * 4.18 * 30

    = 25080J

    Step 2:

    Calculate the relative molecular mass of hexane

    RMM of C6H14 = 86g/mole.

    Step 3:

    Calculate the number of moles of Hexane burned

    Numbrt of mole of hexane = mass / molar mass

    n = 0.5 / 86

    n = 0.0058mole

    Step 4:

    Calculate the enthalpy change of combustion for 1mole

    Combustion of 0.0058mole hexane produces 25080J of heat energy

    I mole hexane produces 25080 / 0.0058

    = 4324kJ of heat energy.

    The enthalpy change of combustion of Hexane is - 4,324kJmol-1.

    There is no need to do anything else for the question.
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