1
$\begingroup$

1-butanol $\ce{C4H10O}$

So I have absolutely no idea how to find the enthalpy and I did some looking on the internet with no use since I don't understand.

I came here hoping someone generous could do the sample calculations so I can understand and do the rest my calculations and test for my experiment.

enter image description here

That's the data for one the mixture of alcohol.

How would I figure out enthalpy for test 1?

(maybe I could cut out test 2, 3 and average in the picture since its irrelevant in figuring out the enthalpy of test 1, and causes confusion)

For temperature before and after. The solution was used to heat up 200 ml of water. By burning the mixture, igniting it.

$\endgroup$
3
  • 1
    $\begingroup$ Welcome to Chemistry Stack Exchange. Can you clarify two things about your question? You want to figure out "enthalpy", but determining the absolute enthalpy is challenging. I assume you are trying to calculate the enthalpy change. Can you verify that is correct? Also, can you tell us a little bit more about this experiment? What procedure are you following? That will help us provide a better answer that is more specific to your situation. $\endgroup$
    – Ben Norris
    Jun 20, 2019 at 12:00
  • $\begingroup$ Yes, I did 5 different mixture of alcohol and water. and we are seeing if the enthalpy changes. That is all. there is 4 more table like this for different mixtures and that is it. I will compare the enthalpy of each solution and talk about it. $\endgroup$
    – user80318
    Jun 20, 2019 at 21:13
  • $\begingroup$ 45 ml of butan-1-ol + 15 ml of water do not have a mass of 156.3–156.5 g. Does the mass include the container? (It also cannot include the additional 200 ml of water that are heated during the experiment.) $\endgroup$
    – user7951
    Jun 23, 2019 at 7:02

1 Answer 1

1
$\begingroup$

Answering your question as it stands is impossible, as we readers do not have enough information about your actual experiment. What do you mean with 'enthalpy of 1-butanol'? You can only measure changes in enthalpy, so you need to specifiy what 'change' you're looking at.

You could mean the enthalpy of evaporation or the reaction enthalpy of some chemical reaction or hundreds of other possibilities. It's essential to clarify what process you're referring to, so one can associate the corresponding starting (e.g. liquid) and end state (-> gas) to this energy change.

However, you stated that 200 ml of solution were heated up by whatever your process was. At constant pressure, the enthalpy required to change the temperature by $\Delta T$ is

$$\Delta H = m c_p \Delta T$$

where $c_p$ is the isobaric heat capacity. Knowing the value of $c_p$, you can calculate this energy change. Now where did that energy come from? Presumably, from your process. At this point, assume that there are no energy losses (f.e. neglect the heat lost to the surrounding air). Then by conservation of energy, the enthalpy increase measured by the temperature increase must be equal in size to the energy released by the process.

Finally, note that by convention we say if a process releases energy, it's enthalpy change is negative (we could've just done it the other way around; think of it as the same idea as defining a sea level).

$\endgroup$
2
  • $\begingroup$ I ignited the solution made a fire that heated up the water. the mass of the fuel was before and after. $\endgroup$
    – user80318
    Jun 23, 2019 at 3:22
  • $\begingroup$ Yes so what you are trying to measure is a enthalpy of reaction (combustion energy). Calculate the energy change as outlined, and then divide that by the mass of fuel that has burnt and you obtain a value of energy released per gram burnt. Best practice would be to calculate this for each test seperately, then average only the final values for the energy content. $\endgroup$ Jun 23, 2019 at 13:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.