Question

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
​

Answer 1

Answer:

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.