5.2/R1.2.2 Hess's Law [SL IB Chemistry]
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- เผยแพร่เมื่อ 23 ก.พ. 2012
- Determine the enthalpy change of a reaction that is the sum of two or three reactions with known enthalpy changes. You don't need to know Hess's Law (!) but you need to be able to use it three ways. The law allows you to work out delta H for reactions, given the delta H for other reactions. You can even work out delta H for reactions that cannot occur. Look up Hess's Law you lazy bum!
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Been 8 years and there is still no better video than this on Hess law.
Sir Richard, saviour of IB chem students everywhere!
I have final exams in 2 days, and as usual you're the hero. (Just completed watching videos of topics which are troubling me, chemistry and chill 😄🤠)
@@areebah8297 I got a 4, since chem was my weakest of all so i am happy w a 4 :)
@@areebah8297 got IB nostalgia after 2 years !
you'll get though this don't worry. ib has definitely helped my batchmates who wanna get into prestigious univeristies in US, UK, singapore etc, but I choosed Germany and IB grade conversion is not really the best, but still I got what I want and if it wasn't IB i wouldn't have known about germany so I am happy w IB @@areebah8297
@@areebah8297 Same situation as you mate :"-))
I am in chem class right now, I dont get anything but I get 100%s in tests thanks to your videos.
IB exam in 5 hours and gonna be dubs thanks to ur videos over the past 2 years 🤟
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another life saved!
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Thank you so much for all your videos. I used to get 2 and 3 in SL chem before, but when I found you on youtube, i am now getting 6 and 7!!!!!!!
Wow - glad I can help!
Richard Thornley I mean in fact, you are already extremely famous for IB Chemistry learners around the world
a legend in my own lunchtime!
Thank you so much. I missed a class day and didn't understand anything at all! but this helps so much! thanks!
Thanks for saving my life Mr. Thornley, id love to play some cs with you just to hang about. Thanks for everything!
i am terrible at CS - i get sniped within 2s every time - TF2 - I am Chemistryrich
Richard Thornley why are you the coolest teacher ever omg
I got the answer for evil wooohooo
Hey, for 6:42, the combustion of ethene equation, I can't balance it so that it goes to 2CO2 + 3H2O.
I'm looking at:
C2H4 + 3O2 --> 2CO2 + 2H2O, but you have down 3H2O instead. The three waters is balanced for combustion of ethanol, but I can't balance it for the combustion of ethene. What am I missing here?
I'm getting the right relationships (tried it using the equations method) for the deltaH's, but I'm not sure what/how to put down that third equation in the cycle. Help?
Oh my god you are saving me. thank you
amazing as always
You just liturally saved my life!! :P
Thank you so much!! This was really helpful to me!!
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Oh my ! If i pass my Chemistry finals it's all because of you Mr. Thornley!
update? lol
I love you man you just saved my life lol THX
thanks so much for this! really explained it well :)
Oooooh, okay, I see now. Thank you!
I wanna ask what is the difference between the heat formation of a compound and its heat content
Thank You Thank You Thank You!
awesome videos!
But in the medium cycle one. the (1/2O2 / -2/3O2 etc.) do we have to know the meaning of them or how to draw them on the cycle?
HI!
Does the rule Delta H = 0 (mentioned at 3:45) not apply to cycle at 4:43?
I understand how the clockwise = counter clockwise rule works here but if we were to use the Delta H = 0 rule here wouldn't "?" be the opposite of the sum of -199 + -4163. Or by the Delta H = 0 rule does it mean clockwise = counter clockwise (and the difference is 0)?
Thanks so much for your videos, and for your response in advance.
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You can replace my teacher
Do you get time to do this videos from the school you work at? If so, I hope they never stop! Your videos make chemistry so much easier... In fact, you boiled down 2 hours worth of teaching in 7min and I got every bit of it, whereas in class it sounded like chinese. Thank you so much!
(side note: what do people who speak chinese say?)
hi! do we have to be able to solve through the energy cycle way? I only know how to do it the first way, should I learn the other way as well..
@ridhajawad You need all 3 ways - equations, cycle and energy diagram
Recently they marked down papers that did not use a cycle.
RT
Hello Mr Thornley! I was just wondering, would we need to know how to use the enthalpy cycles aswell, or are we okay to just know other methods of working out enthalpies?
Thanks :)
Sometimes the IB insists on uses the nasty triangles (cycles) - I sometimes have trouble with them too, but they tend to use the same type each time.
@@ibchemvids man took 5 years to respond
Hey Love your videos, doing Chem myself and find them really helpful!
In the medium one, I did the calculation a couple of times and the answer comes out to be 1415.1.
This just might be me, if your answer is correct could you comment why?
and if you fail we can blame your teacher - hehehe!
hello! for your answer at 5:16 shouldnt it be positive +4362 since the calculations for the clockwise values equal negative -4362 and the Delta H value needs to add up to 0?
spotyheart7 clockwise = anticlock wise -4362 = -4362 ORclockwise - anticlockwise = 0, -4362 - - 4362 = 0 ORgo around clockwise adding up the numbers that are clockwise, subtracting the numbers that are anticlockwise.-199 + -4163 -X =0
I wrote 53.7 but meant to write 537 (i corrected this verbally) - I will fix it with a note now!
yup, make sure you can use your own calculator! If not break the calculation up into smaller bits and be clear on the exam with your working for partial credit.
In regards to the evil one one what do we do with the extra oxygen mole? Don’t we end up with 2.5 moles?
The 3O2 on the arrows is in addition to the lone "O" in the equation - it all balances.
the purple arrow is a little too far left-- you also need to bring the H2O down - then it works
Same and I did exactly what he did as well.
I think there was just a simple problem of summation in the video.
Sir, in the evil one i got -535.4 KJ/mol.
and u got -452.6.
its my bad? i dont know.
5:10 I don’t understand, if the enthalpies are supposed to add up to zero, the why isn’t the new enthalpy found +4362 instead of minus?
They add up zero BUT you need to account for the arrow directions too. An easier way is clockwise arrows = anti clockwise arrows
@@ibchemvids thanks for the reply was 2 years ago. HAHA. Hey check my channel out plz its daniel chuhan (not this one)
if you double the first you will have 1/2 O and if you triple the last you you will have 3/2O well how does it work then ???
@richthornley ok, thanks so much! love your videos - they're hilarious :D
The truly evil part in the evil one was the decimal looking like a multiplication.... I spent like 30 minutes on that
sorry about that!
@nawedy The school gives me about 3-4 hours off a week to do these - not enough really but it keeps me amused !
I got the -2381kJ..it could perhaps be how you're keying the answer into your calculator because I got the same answer as you first time around... but doing a second time as follows:
(-680x2)+(-537x2)+52.3 and I got the right answer.. I think the 2 outside the brackets threw my calculator off
I actually solved the evil question, let's gooooooooooooooo!
do we need to know the triange/cycle way
+Jenna Z The text books thinks so - but the syllabus is unclear :(
at 03:43, all arrow are facing the same direction, isn't that counterintuitive?
That it may be - but it is possible.
I don't like the triangle way but a little while back the IB insisted that it be used , and took off points for the sentence way.
IB Chem is cool :3
no one has ever told me that before (sob) ;)
Chemistry Rich - give me your ID so I know to accept.
PS I have gone cold turkey and not played TF2 for a month - I think I am cured
PPS But I prestiged on BF3 last week!
INTA Fahman
90.4 plus 90.4 plus 46 plus 46 -241.8 - 241.8 - 241.8 = -452.6
It should be :
90.4 plus 90.4 minus 46 minus 46 -241.8 - 241.8 - 241.8 = -636.6
Can you PM me your SteamID? I would love to play some TF2 or CS with you. Thanks!
The cycles are knockoffs of Kirchhoff’s law for circuits