VCE Chemistry Question Thread

[jinaede1342]

Hi, I have a question about galvanic cells. When we are asked to construct/draw a diagram of a galvanic cell, how do we know which pair is the oxidation half equation and vice versa. When we are given a full redox equation we can work it out by assigning oxidation numbers however, I've come across questions such as (Ag⁺/Ag) and (Zn²⁺/Zn) where only pairs such as these are given. How do we know which is which in this instance? Thanks!

[Kadija.Elh]

what exactly are we supposed to know in regards to fuels? do we have to know the process of how fossil fuels and biofuels are produced?

Hey there, according to the study design we need to know the following:
--the comparison of fossil fuels (coal, crude oil, petroleum gas, coal seam gas) and biofuels (biogas, bioethanol,
biodiesel) with reference to energy content, renewability and environmental impacts related to sourcing and
combustion
--the comparison of the suitability of petrodiesel and biodiesel as transport fuels with reference to sources,
chemical structures, combustion products, flow along fuel lines (implications of hygroscopic properties and
impact of outside temperature on viscosity) and the environmental impacts associated with their extraction
and production.
--the definition of a fuel, including the distinction between fossil fuels and biofuels with reference to origin and
renewability (ability of a resource to be replaced by natural processes within a relatively short period of time)
--combustion of fuels as exothermic reactions with reference to the use of the joule as the SI unit of energy,
energy transformations and their efficiencies and measurement of enthalpy change including symbol (∆H) and
common units (kJ mol-1, kJ g-1, MJ/tonne)

[Maya24]

Hi, I have a question about galvanic cells. When we are asked to construct/draw a diagram of a galvanic cell, how do we know which pair is the oxidation half equation and vice versa. When we are given a full redox equation we can work it out by assigning oxidation numbers however, I've come across questions such as (Ag⁺/Ag) and (Zn²⁺/Zn) where only pairs such as these are given. How do we know which is which in this instance? Thanks!

Using the electrochemical series, the very top will undergo reduction and the very bottom will undergo oxidation.

[smamsmo22]

Hi, what is the reason why running an inert gas through a system/fuel cell results in the exclusion of oxygen? I know you want to dispel the oxygen to prevent reaction with products (production of oxides etc) but how does running an inert gas through the cell do this?

[Freddie Hg]

Hi, what is the reason why running an inert gas through a system/fuel cell results in the exclusion of oxygen? I know you want to dispel the oxygen to prevent reaction with products (production of oxides etc) but how does running an inert gas through the cell do this?

hey there!
im sorry, but i havent heard of this. can you refer me to a question or textbook?? i also dont see it in the study design

[hums_student]

Hi, what is the reason why running an inert gas through a system/fuel cell results in the exclusion of oxygen? I know you want to dispel the oxygen to prevent reaction with products (production of oxides etc) but how does running an inert gas through the cell do this?

As far as I know, the inert gas acts to 'flush out' the oxygen in the system. However it's generally not possible to remove all oxygen from the system - it just minimises the amount.

[paranoidchair]

Hey, is this still on the study design? I remember doing similar stuff in Units 1&2 but I don't remember covering it this year

[Lear]

Hey, is this still on the study design? I remember doing similar stuff in Units 1&2 but I don't remember covering it this year
(Image removed from quote.)

No

[Azim.m]

Doesn’t low temperatures prolong battery life, as it decreases the rate for side reactions to occur?

[passbleh24]

Doesn’t low temperatures prolong battery life, as it decreases the rate for side reactions to occur?

Yes it does.
I think I came across this question myself and concluded that it might not be A because of unrealistic conditions ? I'm not too sure because I chose A based on that statement which was incorrect.

[passbleh24]

a - Predict the overall reaction that occurs during electrolysis of a mixture of sodium and nickel (II) using Lead electrodes.
Ni ^2+ (aq) + Pb (s) - Pb^ 2+ (aq) + Ni (s)

b - What voltage would be required for this reaction to occur ?
How would I work this out? The answer is at least 0.1 V and less than 1.46 V. I can't seem to figure out where the number came from.

Thanks

[Azim.m]

a - Predict the overall reaction that occurs during electrolysis of a mixture of sodium and nickel (II) using Lead electrodes.
Ni ^2+ (aq) + Pb (s) - Pb^ 2+ (aq) + Ni (s)

b - What voltage would be required for this reaction to occur ?
How would I work this out? The answer is at least 0.1 V and less than 1.46 V. I can't seem to figure out where the number came from.

Thanks

H20 (reductant- +1.23V) and Ni2+ (-0.23V) can potentially react non spontaneously if the voltage applied is greater than 1.46 V

[crawlingvines]

Doesn’t low temperatures prolong battery life, as it decreases the rate for side reactions to occur?

Yes, but thinking about this question in relation to a mobile phone helped me make better sense of it. Room temp or close to it is the best option.

[passbleh24]

When converting atm to kPa, is 1atm= 101.3kPa or 101.325kPa ?

Hey Just use the data booklet and cross multiply, you can't go wrong with that.
100kpa = 0.987 atm.

According to this 1 atm = 101.317...

[smamsmo22]

Hi, in 2016 students were asked to give the systematic name of ethnic anhydride. Is this still applicable to the current study design (if so, how would we know how to name it?)