Unit 4 Questions MEGATHREAD!

[tony3272]

When a Fe²⁺/Fe half-cell is connected to a Sn²⁺/Sn half-cell, the tin electrode is positive. However, the tin electrode is negative when the Sn²⁺/Sn half-cell is connected to a Fe²⁺/Fe half-cell.

Yeah the information given in the question contradicts itself.

[HenryP]

I think it should be " However, the tin electrode is negative when the Sn2+/Sn half-cell is connected to a Fe2+/Fe3+ half-cell." I think that should make more sense.

[b^3]

Thanks guys, found the answers somewhere and they answered it refering to a Fe³⁺ that they didn't give.

[Christiano]

Lisachem 2008 MC q3 describes hydrogen gas and oxygen gas reacting to form water which is an exothermic reaction.

I picked 'the chemical bonds within the 2 hydrogen molecules and one oxygen molecules are stronger than the chemical bonds within two water molecules' because the energy content of the reactants is greater than the product, which is why heat is released.

But solutions say that reactant bonds in oxygen and hydrogen are weaker than bonds in water molecules. I'm confused, I thought exothermic reactions mean that reactants have more energy content in their bonds, therefore bonds are stronger?

[omgwtf123]

Haiz, you are right in saying that the enthalpy of the reactants in an exothermic reaction would be higher than the enthalpy of the products. However, this makes the bonds in the reactants weaker because as it has a higher enthalpy, the intramolecular chemical bonds are less stable, hence it will take less energy to break these bonds .

Hope i didn't make any mistakes on this >.<

[nbhindi]

Hey guys, I'm really confused as to what we need to know about batteries/Nelson's cell/Downs Cell/ Alkaline Cell/Membrane cell/ Pb acid accumulator....etc. Do we need to memorise/understand how the Leclanche and Daniell cell work, know all the reactions and electrolyes?

Could someone please help me understand as to what cells/batteries we need to know/don't know.
Cheers

[HarveyD]

@person above: pretty sure we dont have to know the reactions, maybe just be aware of how they generally work? so you're prepared in case they ask similar question about it.

anyway, anyone have ideas on how I would do b)ii) of the question below
cant work out why the first two would have 0 mol

[omgwtf123]

did u try including the fact that for the first two beakers, water may be a possible reacting species because of the (aq) state of the compounds?

[HarveyD]

ah yeah, thats it. thanks

[Allygator]

Hey everyone
I'm just marking an exam and disagree with the answer so I was wondering what you guys thought

Question 3 Short Answer Insight 2008
Hydrogen gas and chlorine gas are introduced to a reaction vessel according to the equation
H2(g) + Cl2(g) --> 2HCl(g)
 
b) State the effect of increasing temperature on the pressure within the vessel.
Their solution:
There is the same number of particles on the reactant and product sides of the chemical equation. Neither the forward nor reverse reactions produce more or less particles, so pressure will remain unchanged as the reaction proceeds.

I thought that pressure would increase because even though there are the same number of particles, they have more energy so would exert a greater pressure on the reaction vessel.

Thanks

[REBORN]

This is [u2] ? Higher temperature increases pressure according to the kinetic molecular theory of gases

[Asx4Life]

This is [u2] ? Higher temperature increases pressure according to the kinetic molecular theory of gases

WHAT??!!

[david10d]

it's not in equilibrium so: same number of particles, same volume = no change in pressure.


hmm i don't think there's a change in pressure when there's more chance of the particles colliding. i'm struggling to find an example justifying what i'm trying to say lol

but i could be wrong, my chem is really really average atm..

[nbhindi]

I thought that pressure would increase because even though there are the same number of particles, they have more energy so would exert a greater pressure on the reaction vessel.
Thanks

I did the same paper last week and that's what I had. Here's my logic.....which could be totally flawed  :

From pV=nRT, it is evident that p is directly proportional to the temp, hence increase temp will confer to a higher pressure.

[Mao]

I thought that pressure would increase because even though there are the same number of particles, they have more energy so would exert a greater pressure on the reaction vessel.
Thanks

I did the same paper last week and that's what I had. Here's my logic.....which could be totally flawed  :

From pV=nRT, it is evident that p is directly proportional to the temp, hence increase temp will confer to a higher pressure.

This is exactly right. If the reaction vessel cannot expand, pressure must increase. This is true for any gases. However, the equilibrium will not shift.