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November 01, 2024, 10:25:42 am

Author Topic: VCE Chemistry Question Thread  (Read 2466723 times)  Share 

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rani_b

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Re: VCE Chemistry Question Thread
« Reply #7950 on: March 24, 2019, 07:36:47 pm »
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Hey guys!

"An aluminium cell operates at 4.5 V using a current of 130 000 A with an efficiency of 48%. What mass of Al (kg) would be produced in 24 hours?"

Is it correct to:
- Calculate Q using Q = It
- Calculate n(e) using Q/F
- Calculate n(Al)
- Calculate m(Al) and multiply this by 0.48?

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samyaks123

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Re: VCE Chemistry Question Thread
« Reply #7951 on: March 31, 2019, 02:20:10 pm »
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Does anyone have solutions for last years vcaa exam

If not would you be able to have a look at my responses for the following questions:

Q2a)
Increasing the temperature increases the rate of production of O2. This is because the increase in temperature increases the average kinetic energy of all molecules, increasing the frequency (no. of collisions per second) and energy of collisions between H2O2 molecules. Increasing temperature increases the proportion of successful collisions as more particles have  energy greater than the activation energy, hence increasing ROR

7a)
The reaction mixture is expected to become browner. When the sealed test tube is placed in hot water this increases the temperature of the system. According to LCP, the system will partially oppose the change by decreasing the temperature and favour a net reverse reaction because this is endothermic and absorbs the energy. Thus, the position of equilibrium shifts to the left, increasing the concentration of NO2 and hence the system becomes browner.

b)K=0.060M-1

c) [NO2] will double then decrease by 2 parts, [N2O4] doubles then increases by 1 part

sweetiepi

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Re: VCE Chemistry Question Thread
« Reply #7952 on: March 31, 2019, 02:42:01 pm »
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b)K=0.060M-1
Hey, can you show me your working out for this question? It seems that you've got the right idea, however your value is a factor of 100 off what I'm getting ^-^

Everything else checks out to me btw :)
« Last Edit: March 31, 2019, 02:58:09 pm by insanipi »
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samyaks123

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Re: VCE Chemistry Question Thread
« Reply #7953 on: March 31, 2019, 02:46:30 pm »
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Hey, can you show me your working out for this question? It seems that you've got the right idea, however your value is a factor of 100 off what I'm getting ^-^

Ah, I see, i forgot to account for the * 10-2 given on the y-axis, so it should be 6 right?

sweetiepi

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Re: VCE Chemistry Question Thread
« Reply #7954 on: March 31, 2019, 02:49:24 pm »
+1
Ah, I see, i forgot to account for the * 10-2 given on the y-axis, so it should be 6 right?
That is correct! :) It should be 6 \(M^{-1}\) Don't forget the units! :)
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samyaks123

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Re: VCE Chemistry Question Thread
« Reply #7955 on: March 31, 2019, 03:02:21 pm »
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That is correct! :) It should be 6 \(M^{-1}\) Don't forget the units! :)

Were the responses to those questions fine?

isthately

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Re: VCE Chemistry Question Thread
« Reply #7956 on: April 04, 2019, 06:31:54 pm »
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Hi guys!
I am struggling to study for Chemistry and want to know what is the best way to study for SAC's;
I know this sounds cliche but seriously I don't know what to exactly do. I currently read the subchapter, e.g 3.4. I then go into the key questions for that subchapter and complete them. For notes i just write down the subchapter summary in my book. When i finish the chapter i then go and complete the chapter review. I've had people tell me this isn't efficient. I've also been told to skip the subchapter questions and to just do 'chapter review questions', as the subchapter questions are a waste of time. Also is writing the questions worth it? I see it as a waste of time but also good to look back on.  :-\
I'm hoping that someone who has experienced 3/4 chemistry and received a high study score guide me to the best technique. THANKS!  :)

-_-zzz

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Re: VCE Chemistry Question Thread
« Reply #7957 on: April 05, 2019, 06:34:44 pm »
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Hey guys,

I'm just a bit confused as to why cations flow to the cathode and anions flow to the anode to maintain electrical neutrality within a galvanic cell. It confuses me because, for example, the anode will experience an accumulation of negative charge, so why would anions flow there to 'counteract' this charge? Wouldn't this require cations to flow to the anode?

Thanks in advance.

sweetcheeks

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Re: VCE Chemistry Question Thread
« Reply #7958 on: April 05, 2019, 07:19:51 pm »
+2
Hey guys,

I'm just a bit confused as to why cations flow to the cathode and anions flow to the anode to maintain electrical neutrality within a galvanic cell. It confuses me because, for example, the anode will experience an accumulation of negative charge, so why would anions flow there to 'counteract' this charge? Wouldn't this require cations to flow to the anode?

Thanks in advance.

The anode doesn't accumulate a negative charge, it accumulates a positive charge. Using the Zn/Cu galvanic cell as an example, when oxidation takes place at the anode, the reaction occurring is Zn(s) --> Zn2+ + 2e-. You are getting more positive zinc ions in the solution. You need some sort of negative charge to balance these newly formed positive ions, which is why anions flow towards the anode.

Likewise at the cathode, the copper (ii) ions are being reduced to copper metal, so there would be a net build up of negative charge in that cell, due to the imbalance between anions and cations. Therefore, cations would migrate to the cathode to neutralise the net build up of negative charge.

-_-zzz

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Re: VCE Chemistry Question Thread
« Reply #7959 on: April 05, 2019, 08:25:05 pm »
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The anode doesn't accumulate a negative charge, it accumulates a positive charge. Using the Zn/Cu galvanic cell as an example, when oxidation takes place at the anode, the reaction occurring is Zn(s) --> Zn2+ + 2e-. You are getting more positive zinc ions in the solution. You need some sort of negative charge to balance these newly formed positive ions, which is why anions flow towards the anode.

Likewise at the cathode, the copper (ii) ions are being reduced to copper metal, so there would be a net build up of negative charge in that cell, due to the imbalance between anions and cations. Therefore, cations would migrate to the cathode to neutralise the net build up of negative charge.

Appreciate the response a lot. So when we say that the anode in a galvanic cell has a 'negative polarity' or that it is the 'negative terminal' are we just implying that that is where electrons are being released into the external circuit?

lzxnl

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Re: VCE Chemistry Question Thread
« Reply #7960 on: April 06, 2019, 12:21:14 am »
+1
Appreciate the response a lot. So when we say that the anode in a galvanic cell has a 'negative polarity' or that it is the 'negative terminal' are we just implying that that is where electrons are being released into the external circuit?
Think of it as where electrons don't want to be. For an electron, a negative terminal is like a high cliff, scary with a lot of potential energy. A positive terminal is a lower cliff, much safer and less scary. In a galvanic cell, with no external energy input, the electrons fall from high to low potential energy, which is negative to positive terminals. In an electrolytic cell, the energy throws the electrons up the cliff and reverses the reaction, pushing them where they really would rather not be.
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jollyboat

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Re: VCE Chemistry Question Thread
« Reply #7961 on: April 11, 2019, 06:09:54 pm »
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Hey

I'm confused about why we extrapolate out lines on temperature-time graphs to get delta T values for calorimetry. I get that it's to make up for the fact that calorimeters are not perfectly insulated - but I thought the whole reason we use calibration factors was to make up for the calorimeter not being perfectly insulated, so why bother extrapolating out to get the delta T value as well?

Hope this makes sense. Thanks :)

peachxmh

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Re: VCE Chemistry Question Thread
« Reply #7962 on: April 12, 2019, 06:11:59 pm »
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Hey guys, do Maxwell-Boltzmann distribution curves have to start at the origin and why/why not? Can it start at 0 on the x-axis but be higher on the y-axis (e.g. can it start at (0,2) -> lol idk how to explain other than using coordinates), or can it start at 0 on the y-axis but be further right on the x-axis? (e.g. can it start at (2,0)). Thank youuuuuu!
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-_-zzz

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Re: VCE Chemistry Question Thread
« Reply #7963 on: April 12, 2019, 10:46:21 pm »
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Hey guys, do Maxwell-Boltzmann distribution curves have to start at the origin and why/why not? Can it start at 0 on the x-axis but be higher on the y-axis (e.g. can it start at (0,2) -> lol idk how to explain other than using coordinates), or can it start at 0 on the y-axis but be further right on the x-axis? (e.g. can it start at (2,0)). Thank youuuuuu!

Yes they have to start at 0. Consider what the Maxwell-Boltzmann curve actually describes: the distribution of kinetic energies within samples of substances. Thus we must also show that there are NO particles with ZERO kinetic energy in any sample.

Hope that helps :)
« Last Edit: April 25, 2019, 01:57:52 pm by -_-zzz »

peachxmh

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Re: VCE Chemistry Question Thread
« Reply #7964 on: April 13, 2019, 10:00:15 pm »
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One more question - in the Heinemann Chem textbook, it says that the "dilution of an aqueous equilibrium system has no effect on the value of Kc for the reaction". I don't understand this - isn't the system shifting to the side of the reaction with the greater mol in order to increase the concentration of the solution (which reduced bc of the dilution). In that case, wouldn't Kc be affected since a shift has occurred and one side of the reaction is being favoured more than the other compared to before the dilution occurred? Thanks :D

Edit: Is it just temperature that affects the Kc value? If so, why? I thought that adding/removing reactants/products and changing pressure by changing volume would also change the Kc value since in both scenarios a shift has occurred.
« Last Edit: April 13, 2019, 10:06:51 pm by peachxmh »
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