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

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.

the right answer is c i just did the question.

a). in this case, dh> 0 and sd> 0. if t becomes larger, the term "-tds" will become more negative. at some point, it is possible that -dts will be more negative than the dh is positive, and the reaction will become spontaneous. this is probably the correct answer, but you should look at all of the other possibilities and make sure of that.