A 1.00 g sample of n-hexane (C6H14) undergoes complete combustion with excess O2 in a bomb calorimeter. The temperature of the 1502 g of water surrounding the bomb rises from 22.64°C to 29.30°C. The heat capacity of the hardware component of the calorimeter (everything that is not water) is 4042 J/°C. What is ΔU for the combustion of n-C6H14? One mole of n-C6H14 is 86.1 g. The specific heat of water is 4.184 J/g·°C.

The combustion of n-hexane in a bomb calorimeter is an adiabatic process, which means that the heat released by the reaction (q reaction) is absorbed by the calorimeter (q absorbed). The heat is absorbed in part by the hardware component of the calorimeter (Ccal= 4042 J/ºc) and in part by the surrounding water (Cw= 4.184 J/ºC). In a process at constant volume, the heat is equal to the variation of internal energy (ΔU). Thus, we have:

ΔU= - q reaction = q absorbed = qcal + qw

We calculate first the heat absorbed by the calorimeter (qcal):

qcal= Ccal x ΔT

qcal= 4042 J/ºC x (29.30ºC - 22.64ºC)

qcal= 26919.72 J

Secondly, we calculate the heat absorbed by the water (qw)

qw= m x Cw x ΔT

qw= 1502 g x 4.184 J/g.ºC x (29.30ºC - 22.64ºC)

qw= 41853.9 J

q absorbed = qcal + qw = 26919.72 + 41853.9 J = 68773.61 J

This amount of heat is released by 1 g of n-hexane. To calculate ΔU we use the molecular weight of n-hexane (86.1 g/mol):

ΔU = q absorbed = 68773.61 J/ 1 g x 86.1 g/ mol x 1 KJ/ 10³ J = 5921.4 KJ/mol

nikitarahangdaleVT nikitarahangdaleVT · Answer 2 · 2022-03-23T06:48:06+01:00

5921.4 KJ/mol is ΔU for the combustion of n-hexane.

What is combustion reaction?

Combustion reactions are those reactions in which oxidation of fuel takes place in the presence of oxygen to form water and carbon dioxide.

Given reaction is the adiabatic reaction means no heat is evolved from the whole set up.

Heat capacity of hardware component of the calorimeter = 4042 J/°C

Heat capacity of water = 4.184 J/g·°C

Heat of the reaction at the constant volume is equal to the change in internal energy and this will be calculated as:

ΔU= - q released = q absorbed = qc + qw

So, heat absorbed by the calorimeter will be calculated as:
qc = C x ΔT

qc = 4042 J/ºC x (29.30ºC - 22.64ºC) = 26919.72 J

Heat absorbed by the water will be calculated as:
qw = m x Cw x ΔT

qw= 1502 g x 4.184 J/g.ºC x (29.30ºC - 22.64ºC) = 41853.9 J

Hence, total heat absorbed:

q absorbed = 26919.72 + 41853.9 J = 68773.61 J

Heat absorbed by the calorimeter is released by the 1 gram of n-hexane

Heat released by 86.1g of n-hexane = 68773.61 J/ 1 g x 86.1 g/ mol x 1 KJ/ 10³ J = 5921.4 KJ/mol

And this 5921.4 KJ/mol amount of heat will be equal to change in internal energy.

Hence, 5921.4 KJ/mol is the value of ΔU.

To know more about combustion reaction, visit the below link:

https://brainly.com/question/9425444