Lab Report Graphing: Photo Editing?

[dessskris]

I did an Energetics lab and I need to plot the temperature against time graphs.

In both experiments we reacted a solid and an aqueous solution. We monitored the solution's temperature for 120 s and then add the solid. We needed to monitor the temperature every 30 s until it has reached its maximum/minimum.

The problem is that our teacher keeps telling us that our graphs are wrong. The graph should be something like the picture below:

It is first constant, then significantly increasing (as they react) and gradually decreasing to reach room temperature. Then create a linear trendline when the graph is decreasing to get the ΔH.

The problem is that we monitored the temperature until it has reached its maximum/minimum so after it increased significantly I only have 1 more data point so I cannot create that linear trendline.

So I thought I would just take the maximum/minimum point of the graph and take the difference between the initial temperature and that max/min temp.

But I still have another problem. I am supposed to have a straight line in the beginning and then a parabola. Excel can't give me one nor can TI-Nspire do it. I once asked my teacher about this in another lab and she told me to draw the graph by hand and scan and paste it there. We don't need the equation of the graph anyway.

Can I do that? If yes, can I draw the graph on computer? I plotted the data points using TI software and use photoshop to draw the curve. Like in paint you can drag your mouse to draw it, right? In photoshop you can use Pen Tool to create a path and modify the path to make it look like a perfect curve. Can I do this? It's similar to drawing one by hand.. I am just afraid if this kind of graph is not acceptable. So can I do this? Thank you.

[genepeer]

I did those graphs by hand, but since they encourage us to use technology, I suppose they'd allow us to draw it digitally. You do have a problem with your data-set though. One point isn't enough to draw the line of best fit. Not a good advise but you can still let this IA slide, they only pick your best IAs anyway. If you can't do that, then get the data from a friend or forge it. I do have an IA or two I handed in that barely made any sense.

[dessskris]

Haha great then thanks

Yeah and in experiment 2 I have no data point after my maximum I have one after my minimum in experiment 1

Problem is my teacher have looked at our first draft so I cannot manipulate my data sets in any way

Is there any other way to find the change in temperature? Can't I just take my max/min temperature and minus it from my initial temperature?

This is the procedure's fault! I have done a number of energetics experiments and they always ask us to stop recording the temperature after it has reached its maximum/minimum!!!

[genepeer]

Well, when the reaction occurs, it's assumed all energy is released almost instantaneously. But the water doesn't absorb it all at once; as it gradually increases temperature, some heat is lost to the environment so in the end, the maximum temperature you measure isn't the theoretical maximum temperature. So we assume the loss of temperature is constant (technically, this is wrong. it's exponential), so we extrapolate by drawing a straight line. So even though, "final T" in that diagram isn't the true theoretical maximum, it's still a better approximation than your current maximum.

So to answer your question, I don't think there's another way. However, you can use the maximum you have, your results on enthalpy change will be way off from expected results and then you mention the error you made in your evaluation. Or you can repeat the experiment.

[dessskris]

Ohhh I didn't know that! Teacher never explained it to us

Amazing advice, I will just put it in my CE. I don't get why teacher wants us to change our graphs knowing there is no other way to do that

Thank you very much!