[matt1234]

Hello,
Im working on a project where im required to compare the enthlpy change of combustion between hydrogen and octane.  The results will be used later in a  report where i compare the hydrogen fuel cell as an alternative to gasoline for cars.  I have to design my own procedure for using a bomb calorimeter.  The method i have used so far for measuring the samples was by volume.

My question is:
What is the best way to compare the two fuels in a bomb calorimeter, by equal mass? Say 1 gram of hydrogen and 1 gram of octane at SATP? OR 1 mol of each at SATP?

The reason i ask was because I was trying to use 1 gram of octane and 1 gram of hydrogen but the volume of 1 gram of hydrogen at SATP is way too big for a bomb calorimeter. 11.125 Litres.

Yet, if i use 1 mol of each there volumes nor their masses will match. Not to mention 1 mol of hydrogen is 22.4 Liters.  Using 1 gram above i am using approx half a mole of hydrogen.

Please advise.  

I have another question which is confusing me, since im required to compare combustion of hydrogen and octane should i compare H2 as its found in nature or just H?

[billnotgatez]

Can you use the max amount of hydrogen that can fit in your calorimeter and then use the same moles of octane?

[matt1234]

I will not actually be performing the experiment, so i have not chosen a make and model of a calorimeter, so im not sure what the max would be. 

So far how i have written the procedure is as follows:

1 gram of each substance, for octane i CAN specify the volume at SATP but for hydrogen i cannot since i dont know the pressure from the tank.  So i referred to the ideal gas law in the procedure. 
What do you guys think of my attempt?

[408]

You are able to use differing amounts of each, and still have directly comparable results if you simply convert to kJ/mol instead of simply kJ.

You also cannot simply fill your calorimeter with just hydrogen and expect it to work, you need oxygen present.  You also need to know if your calorimeter can handle the pressure generated by a mix of hydrogen and oxygen combusting... I imagine a good, metal calorimeter can handle this, but gas explosions have surprised me in what they can do in the past...

[matt1234]

So i can compare the molar enthalpy, which I understand.  Now 1 gram of hydrogen gas is approx half a mol  so i think ill stick with the 1 gram of each sample.

Now i need to find empirical values for delta T for the combustion of hydrogen and octane (or gasoline) so i can perform the "virtual experiment" we were asked to do.  

Anyone have an idea where i can get delta T for a specific bomb calorimeter for a sample of hydrogen and octane of ANY mass?  Im not sure if people have done this or even make their labs public..

[Aliyah786]

have you figured out how to get delta T?