VCE Chemistry Question Thread

[Yacoubb]

Just to make sure as the book doesn't explicitly state that there is a salt bridge involved in electroplating however mentions NO3- balances the charge. Are salt bridges involved in electroplating?

Stupid question I know -.- thanks!

Based on my understanding, electrolysis occurs in electroplating, and salt bridges are not involved in electrolysis.

In the electrochemical series, what do the potential values actually mean? Like, why doesn't a reaction occur if the E(highest) - E (lowest) is a negative number?

thanks

I was actually wondering the same thing... to be honest, I'm just going to know that spontaneous reactions occurs with + E naught values, and non-spontaneous reactions have -ve E naught values

[Rishi97]

I was actually wondering the same thing... to be honest, I'm just going to know that spontaneous reactions occurs with + E naught values, and non-spontaneous reactions have -ve E naught values

Yeah that's all I wanted to memorise too but there is a question on the 2011 paper which requires us to write why the reaction won't occur so I'm a bit confuzzled :/
Anyone know?

[Reus]

Thanks Yacoubb

[Yacoubb]

Yeah that's all I wanted to memorise too but there is a question on the 2011 paper which requires us to write why the reaction won't occur so I'm a bit confuzzled :/
Anyone know?

Hmm, was the question something along the lines of why a reaction wont occur even if its spontaneous according to the electrochemical series? Or was it asking why a reaction wont occur between two species?

Thanks Yacoubb

It's all good

[Rishi97]

Hmm, was the question something along the lines of why a reaction wont occur even if its spontaneous according to the electrochemical series? Or was it asking why a reaction wont occur between two species?

wait..i think I read the question wrong. The question basically provided a table with the reaction and E values. Then it asked why the reaction is not predicted to occur to any significant extent.
I thought it was to do with E values but they just wanted us to write which products will be formed -_-
#chemlife

[lzxnl]

Based on my understanding, electrolysis occurs in electroplating, and salt bridges are not involved in electrolysis.

I was actually wondering the same thing... to be honest, I'm just going to know that spontaneous reactions occurs with + E naught values, and non-spontaneous reactions have -ve E naught values

Let's say you have A being oxidised to A+ + e-
and you have B + e- being reduced to B-
so overall reaction of A + B => A+ + B-
Let the reduction potential of B + e- => B- be E1 and let the reduction potential of A+ + e- => A being E2. Note: the second reaction is given as the reverse of the oxidation of A.
Then, E1 - E2 is the cell potential, which I will denote by Ecell. Using thermodynamic arguments, it can be shown that for the system we have here, Ecell = RT/F * ln K, where K is the regular equilibrium constant and F is one Faraday, or 96485 C/mol. Hence, if your Ecell is negative (i.e. your oxidant is below your reductant on the electrochemical series), ln K < 0 => K < 1, an unfavourable reaction.
If you just plug in Ecell = 1 V, you'll find that K is huge. Therefore, large negative values of Ecell will give you tiny values of K and this is why we say those reactions don't occur.

But of course, VCAA expects you to just accept what you've been told without knowing why.

wait..i think I read the question wrong. The question basically provided a table with the reaction and E values. Then it asked why the reaction is not predicted to occur to any significant extent.
I thought it was to do with E values but they just wanted us to write which products will be formed -_-
#chemlife

Do you have the question?

[soNasty]

What can we deduce about a reaction whereby Equilibrium constant values are the same for both the forward and reverse reactions?

[lzxnl]

What can we deduce about a reaction whereby Equilibrium constant values are the same for both the forward and reverse reactions?

The equilibrium constant must be 1 as K(forward) = 1/K(reverse)

[Reus]

Why does the presence of a strong acid in the electrolyte allow higher rates of tin plating than a weak acid?

[Brunette15]

Can someone please help me with this question:

You are provided with the following information in addition to that found in the Data Booklet

H2O(s) --> H2O(l) Enthalply= +6.00kJ/mol
H2O(l) --> H2O(g) Enthalply= +44.0kJ/mol

The energy (in kJ) required to convert 1.0 mol of ice at zero degrees to 1.00mol of steam at 100 degrees is closest to
A,15
B,50
C,60
D,7500

The answer is C...

[sparksfly]

For the ionisation of HOCl, the equilibrium reaction has the same number of particles on both sides:
HOCl + H20 ««»» H30+ + OCl-

So when you dilute a certain sample, will there be a net forward/ backward reaction? I'm dont understand why the answers says there'll be a net forward reaction- am I missing something here?

Any help would be great 

[BLACKCATT]

For the ionisation of HOCl, the equilibrium reaction has the same number of particles on both sides:
HOCl + H20 ««»» H30+ + OCl-

So when you dilute a certain sample, will there be a net forward/ backward reaction? I'm dont understand why the answers says there'll be a net forward reaction- am I missing something here?

Any help would be great 

Yeah there will be. Since all reactants/products are aqueous, except for H2O(l), then the system will act to oppose this change by favouring the reaction that increases the concentrations of aqueous solutions (forward reaction). This is because only the products are aqueous.

[Rishi97]

Do you have the question?

It was the VCAA 2011 Exam 2 Q4...the really badly answered one
But I understand it now
Thanks anyways

[ETTH96]

When a galvanic cell is being recharged, is it the anode reaction that is reversed? how come the cathode isn't reversed as well? What about in electrolysis? Thanks

[BLACKCATT]

Why is the energy part 100/65? Isn't it meant to be 65/100