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zhangs or ace for CHEMISTRY? (3 Viewers)

eternallyboreduser

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dang but still a high mark. bruh circling the wrong bubble is just sad
bruh legit and misreading the q too, although i can accept this one circlinf thr wrong bubble is depressing. imma start circling on the actual sheet first cos usually i circle it on the paper and then copy it down onto the mcq sheet 😭😭
 

enip

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bruh legit and misreading the q too, although i can accept this one circlinf thr wrong bubble is depressing. imma start circling on the actual sheet first cos usually i circle it on the paper and then copy it down onto the mcq sheet 😭😭
which q did u misread
 

eternallyboreduser

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yeah the average was around 80-85 so you chilling. also i heard that if top. 50, then we get a bonus/discount but not 100% certai. have u heard ???
damnn rlly? That would be sick if it’s true but ive never heard of that
 
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eternallyboreduser

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yeah the average was around 80-85 so you chilling. also i heard that if top. 50, then we get a bonus/discount but not 100% certai. have u heard ???
My class average was like in the high 70’s i think lol
 

Luukas.2

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don't have the paper to show but question was like why is cyclopropane more reactive than propane (with diagram)
That's a good question, though not one that really fits inside the HSC syllabus.

Ring strain is a destabilising factor for ring systems except when they have six atoms in the ring - Wikipedia has an article about it - and the problem with bond angles away from the ideal tetrahedral angle is intuitively obvious. The contribution from eclipsed rather than staggered conformations is also not difficult to appreciate in a qualitative sense, though the syllabus does not really go into those areas either.

The effect can be seen in its reactivity, for example. Cyclopropane reacts with HBr to yield 1-bromopropane, an addition reaction that is akin to the behaviour of propene but not propane.

Quantifying the effect of ring strain is well beyond the syllabus, though quantified effects can be seen in the elevation of the enthalpies of combustion. Estimating the enthalpy of combustion from bond energies for cyclopropane (in gas phase) gives:

Cyclopropane: C3H6 (g) + 4.5 O2 (g) ---> 3 CO2 (g) + 3 H2O (g)


Adjusting back to standard states by using:

H2O (g) ---> H2O (l)

gives an estimate of the enthalpy of combustion as .

The actual value is .

This 150 kJ mol-1 difference reflects that the three strained carbon-carbon bonds in the cyclopropane ring are weaker than a typical carbon-carbon bond. In fact, assuming that the strain only affects the carbon-carbon bond strength (which isn't true, but the effect on the carbon-hydrogen bond strengths will be significantly smaller in magnitude), we can calculate:


In other words, compared to the typical / average BE(C-C) = +348 kJ mol-1, the carbon-carbon bonds in cyclopropane are only about 75% as strong.

There is the basis for a good, challenging, question that builds on content in modules 1, 4, and 7 (at least).
 

Inhstwant99.95atar

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hi, I go to PEAK for chemistry (year 11), but I want to change next term. I was thinking either Zhangs or Ace. I also thought matrix but i heard that they were a bit on the easier side (not 100% sure about that tho). Anyways can someone who went to either or them, or just in general suggest which one would suit me. I am looking for an organised tutoring which is more on the harder end, like having harder homework and exams. thanks
Whats’s wrong with peak?

I currently attend Year 12 lessons for chemistry there, and I find that the content they teach you is “all you need to know,” places like matrix like to waffle a lot. However, I did see zhang’s state ranks look very appealing, but the theory is very hard to look at (looks like a textbook).

They also like throwing you straight into hard questions, which makes you actually think. No spoon feeding haha.
 

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