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/sci/ - Science & Math

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2097411 No.2097411 [Reply] [Original]

Why can't the heat of reaction for the combustion of magnesium be measured directly? Is it because the reaction is exothermic?

>> No.2097448

It can be. I do this in lab all the time.

>> No.2097442

bump

>> No.2097481
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2097481

>>2097448
Then what is this lab talking about then? Apparently we can't measure it directly.

>> No.2097506

>>2097481
I'm referring to question 3, by the way.

>> No.2097519

>>2097506
Might relate to your particular experiment.

>> No.2097522

Heat + Mg + O2 -> .... + heat

Heat is on both sides of the equation.

No, I won't do the rest for you.

>> No.2097523

>>2097481
First year chem?
We just did the exact same experiment with the same compounds.

>> No.2097533

>>2097523
Indeed it is, we just started thermochemistry too.

>>2097522
So it has to do with heat on both sides of the equation? I thought it was exothermic, so heat was just on the one side.

>> No.2097568

>>2097533
The convenient thing about learning this stuff in school is that you learn as you go. Very recently you should have touched on initial energy of a reaction/catalysts, and differentiating between endothermic/exothermic reactions.

This reaction is very common for a lab because it isn't as straightforward as combustion of say, cellulose.

>> No.2097593

>>2097568
Okay, makes sense. Thanks.

Further questions:
4. The formula is Q = mCΔT
5. The specific heat capacity of water is 4.18 J/(g·C)
Are these correct?

>> No.2097613

>>2097593
Yeah, seems about right for an intro course. It'd be a bit different if you were using a calorimeter. I'm assuming you're just using a thermometer though...?

>> No.2097621

>gen chem lab
you will learn not to give a single fuck about this type of shit by your 3rd year.

>> No.2097625

>>2097613
Yeah, no calorimeters for us.

>> No.2097636

>>2097621
I can't wait until then, I'm sick of prelabs.

>> No.2097663

>>2097636
>implying write-ups aren't worse/more time consuming

>> No.2097677
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2097677

>>2097663
>If I see that analysis one more fucking time

Also, question 7: I assume this is the value I'm to use?

>> No.2097697

>>2097677
Yes.
Didn't you cover the basics of thermodynamics in high school?

>> No.2097703

>>2097697
Yes, but we barely touched on thermodynamics (read: Q=mCΔT is all we learned)