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July 23, 2025, 01:45:50 am

Author Topic: Reaction graphs  (Read 1572 times)  Share 

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chemkid_23

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Reaction graphs
« on: July 11, 2011, 10:23:03 pm »
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So we had to graph our results of:
- temperature v time
- temperature vs 1/time
- concentration vs time
- concentration vs 1/time

time or 1/time is always on the X axis

For each graph vs time, the line of best fit sloped down. (decreases)
For each graph vs 1/time, the line of best fit sloped up (increases)

So is that correct? I just ned confirmation.
Thanks guys

jane1234

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Re: Reaction graphs
« Reply #1 on: July 11, 2011, 10:50:02 pm »
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I'd put time or 1/time on the vertical axis as it is the dependent variable.

And yes, the time should decrease and 1/time should increase but take note that these won't necessarily all be straight lines. The time will probably be curved for both (appearing to exponentially decrease) and the 1/time may be a straight line or a curve. Temperature is more likely to give curves for both (this is what we found anyway). :)

chemkid_23

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Re: Reaction graphs
« Reply #2 on: July 11, 2011, 11:06:49 pm »
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ye we had to explicitly put time on X axis, teachers told us to.
And we had to fit a line of best fit.

jane1234

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Re: Reaction graphs
« Reply #3 on: July 11, 2011, 11:32:30 pm »
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ye we had to explicitly put time on X axis, teachers told us to.
And we had to fit a line of best fit.


X axis as in horizontal? Because usually you would put the independent variable there...

And the time it will decrease a bit like a hyperbola so if your teacher wants you to draw a line then it won't fit very well...

Nonetheless, it is your teacher so for SACs just do what he/she says but I question why they would draw a line when it clearly isn't.

Graphite

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Re: Reaction graphs
« Reply #4 on: July 12, 2011, 11:12:58 pm »
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I don't understand why time or 1/time is the dependent variable. Don't get confused with methods thinking its a reciprocal function. Its simply using linear regression to transform the graph into a linear one.

stonecold

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Re: Reaction graphs
« Reply #5 on: July 12, 2011, 11:15:41 pm »
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I don't understand why time or 1/time is the dependent variable. Don't get confused with methods thinking its a reciprocal function. Its simply using linear regression to transform the graph into a linear one.

Time is the dependent variable because the reaction time depends on the temperature/concentration and NOT vice versa.
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jane1234

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Re: Reaction graphs
« Reply #6 on: July 12, 2011, 11:21:16 pm »
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I don't understand why time or 1/time is the dependent variable. Don't get confused with methods thinking its a reciprocal function. Its simply using linear regression to transform the graph into a linear one.

Hence why I said it looks "a bit like" a hyperbola.

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Re: Reaction graphs
« Reply #7 on: July 12, 2011, 11:29:10 pm »
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Yea but in an exothermic reaction, as time proceeds, temperature increases and vice versa for an endothermic reaction

jane1234

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Re: Reaction graphs
« Reply #8 on: July 12, 2011, 11:33:46 pm »
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Yea but in an exothermic reaction, as time proceeds, temperature increases and vice versa for an endothermic reaction


Ah I see the confusion here.

You can take the OP's post either way.
If you heat/cool the mixture yourself to change the reaction rate then time will be the dependent variable, not the independent.
If you measure the temperature as a means of showing the progressing reaction then, yes, time would go on the horizontal axis.

Same goes with concentration.

chemkid_23, which one was it?

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Re: Reaction graphs
« Reply #9 on: July 12, 2011, 11:36:24 pm »
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If the experiment was to measure the time a reaction took place per unit time at a given temperature, then that would be extremely impractical

Mao

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Re: Reaction graphs
« Reply #10 on: July 12, 2011, 11:56:17 pm »
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Short answer: do as the question says. There is no ambiguity.



Long answer:

This has little to do with independent and dependent variables. This is a coordinate transformation, which transforms a curve into a linear line so a line of best fit can be drawn (because no one is capable of drawing a hyperbola of best fit). The resulting linear line has two easily determinable parameters: the gradient and y-intercept. A formula would then be provided to interpret these quantities. Such interpretation only works when x and y are as specified by the transformation.

In this case, the transformation requires t and 1/t to be on the x axis. Regardless of which is the independent variable, the interpretation dictates that the graph must be set up this way.

(Of course, you can transpose the linear fit to take the inverse, etc etc.)
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Mao

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Re: Reaction graphs
« Reply #11 on: July 13, 2011, 12:08:26 am »
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For each graph vs time, the line of best fit sloped down. (decreases)
For each graph vs 1/time, the line of best fit sloped up (increases)

Yes. The slope always change signs when you go from vs t to vs 1/t.
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chemkid_23

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Re: Reaction graphs
« Reply #12 on: July 13, 2011, 03:21:58 pm »
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Mao is right, do as the question asked; which is what I did.
The teacher stated on the sheet she gave us to put time and 1/time on the X axis; don't ask why, she just told us to. If she marks it wrong, I'll show her the sheet. No biggy

Bozo

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Re: Reaction graphs
« Reply #13 on: July 31, 2011, 08:35:02 pm »
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hey so what type of questions did they ask you for the write up of this sac?