Bazza's 3/4 chemistry questions

[WhoTookMyUsername]

Thanks:)

How come when the temperature is raised, the highest number of particles for a given temperature ( average temperature ) decreases?


2) with my earlier question, the textbook keeps emphasising it

The energy change for the reaction is the difference between the energy absorbed to break the bonds in the H2 and O2 reactants, and the energy released when the bonds in the H2O product are made.

"energy released when the bonds are formed" is this correct? Is it just bad phrasing? Is the energy released due to the previous bond breaks, and some of this is reused to form new bonds?

What exactly is going on in a reaction like this?

Thanks

[Deleted User]

Is that Nick Powell? (ie another ovverrated English kid)?

[Graphite]

Thanks:)

How come when the temperature is raised, the highest number of particles for a given temperature ( average temperature ) decreases?


2) with my earlier question, the textbook keeps emphasising it

The energy change for the reaction is the difference between the energy absorbed to break the bonds in the H2 and O2 reactants, and the energy released when the bonds in the H2O product are made.

"energy released when the bonds are formed" is this correct? Is it just bad phrasing? Is the energy released due to the previous bond breaks, and some of this is reused to form new bonds?

What exactly is going on in a reaction like this?

Thanks

Probs because as you have a higher temperature there is a greater temperature range with the same number of particles. Yes it's correct to say energy is released when bonds form. Look at an energy profile and this would become fairly apparent. As you move up the hump, the energy is consumed which is why the energy f the system ncreases. As the hump declines, energy is released which is why the energy of the system decreases.

[WhoTookMyUsername]

Do we need to memorise the sulfuric acid equations like the conversion of calcium phosophate to superphosphate?
Thanks

[thushan]

Do we need to memorise the sulfuric acid equations like the conversion of calcium phosophate to superphosphate?
Thanks

yes

[paulsterio]

I just think you'd be silly to remember calcium phosphate -> superphosphate when you could just remember the ammonium sulfate one

[charmanderp]

If you're talking about the question from last year's unit 4 exam, the most obvious answer to use would be sulfuric acid and sulfur trioxide to produce oleum.

[WhoTookMyUsername]

Chem chem chem! i'm a bit rusty in some areas... Trying to fix it

1) How do you know which water half equation to use for galvanic cells? Is it usually the hydroxide one?
2) for Lead sulfate PbSO4 how do you determine the oxidation numbers? Most electroneg takes number equal to charge, so O takes -2, is Pb 2+ then? Do you tret SO4 as one unit in this case? (with overall charge 2- )
3) when a question refers to the " instantaneous rate of forward reac" is this the instantly immediate rate of forward reaction or the instantly immediate Rate of NET forward reaction
For e.g. If you increase pressure of an equilibrium system that has 1 molecule of gas on left and 2 molecules of gas on right, the NET instantenous forward reac rate will be decreased, whereas the instantaneous forward reaction rate itself will be increased?
4) does equilibrium system mean a sytem at equilibrium or a system with the potential to reach equilibrium?
5) on the vcaa 08 exam it refers to the production of hydrogen gas from sulfuric acid, is this utilising zinc or aluminium ?( useful product of sulfuric acid)


I know these questions are quite basic but would be great if someone could shed light on these!
Thanks

[charmanderp]

1) In galvanic cells water rarely reacts as it is a weak oxidant and reductant. However in both electrochem and electrolysis, it's not 'usually the hydroxide one' or the hydronium one; it depends on what type of conditions are present (acidic or basic). Doubt you'll get a question which involes water as an oxidant/reductant in a galvanic cell though.
2) Yeah Pb is +2 for the reasons that you've listed.
3) Don't really understand this question but presumably that means the rate of forward reaction at any one point of the reaction, like calculus.
4) Equilibrium system is a system which is at its equilibrium.
5)A question number would be helpful.

[WhoTookMyUsername]

thanks

2) Would you always treat a polyatomic ion as a single "unit" in what cases is this viable? (sorry i'm not that specific, i'm a bit confuzzled lol)
3) AT any one time you have forward reaction occuring and backward reaction occuring; but at equilibrium the reaction rates are equal. So NET forward reaction rate is 0 but forward reaction rate is > 0. when a question refers to the " instantaneous rate of forward reac" is this the instantly immediate rate of forward reaction or the instantly immediate Rate of NET forward reaction
For e.g. If you increase pressure of an equilibrium system that has 1 molecule of gas on left and 2 molecules of gas on right, the NET instantenous forward reac rate will be decreased, whereas the instantaneous forward reaction rate itself will be increased?

5) it was just a general "list one useful product of the substance you ahve chosen (sulfuric acid) then write the equation of the production of this product"

[charmanderp]

2) Yes, you're heading down the right path with that line of thinking.
3) I am utterly confused. I think what you've said is correct.
5) You could use either aluminium or zinc, but with zinc the ratio to sulfuric is 1:1, whereas with aluminium it's 3:2.

[WhoTookMyUsername]

Not sure about the reasoning for the following question D:

19)
Nickel-hydrogen (Ni-H2) batteries.... yada yada.... use KOH as an electrolyte.
The cathode is made from porous nickel plaque which contains nickel hydroxide, NiO(OH)
The anode includes a Teflon-bonded plantinum black catalyst
The reaction occurring at the (+) electrode when this battery is delivering energy is
NiOOH9s) + H20(l) + e- -> NI(OH)2 + OH-(aq)
The reaction at the electrode (-) is most likely to be

c) H2(g) -> 2H+ (aq) + 2e-
d) H2(g) + 2OH-(aq) -> 2H20(l) + 2e-

Not sure how to differentiate between these two.
The answers say
"Since the electrolyte is alkaline, the oxidation half-equation must contain OH-(aq) ions"
Why is this the case?
The electrolyte is KOH which is the same for all simple galvanic cells... most of which don't involve OH-(aq) as a reactant?
Am i missing something here?
thanks!

[Conic]

Don't most of the simple galvanic cells use NaCl or KNO3?

[WhoTookMyUsername]

c) H2(g) -> 2H+ (aq) + 2e-
d) H2(g) + 2OH-(aq) -> 2H20(l) + 2e-

Not sure how to differentiate between these two.
The answers say
"Since the electrolyte is alkaline, the oxidation half-equation must contain OH-(aq) ions"
Why is this the case?
The electrolyte is KOH which is the same for all simple galvanic cells... most of which don't involve OH-(aq) as a reactant?
Am i missing something here?
thanks!

KOH isn't the electrolyte for all simple galvanic cells.

Yep my bad, confused KOH with KNO3 =.=

I think my question still stands though, why does OH HAVE to be part of the reaction? OH could still perform it's function simply in balancing out the resultant charges at the oxidation electrode couldn't it?

Not sure about the reasoning for the following question D:

19)
Nickel-hydrogen (Ni-H2) batteries.... yada yada.... use KOH as an electrolyte.
The cathode is made from porous nickel plaque which contains nickel hydroxide, NiO(OH)
The anode includes a Teflon-bonded plantinum black catalyst
The reaction occurring at the (+) electrode when this battery is delivering energy is
NiOOH9s) + H20(l) + e- -> NI(OH)2 + OH-(aq)
The reaction at the electrode (-) is most likely to be

c) H2(g) -> 2H+ (aq) + 2e-
d) H2(g) + 2OH-(aq) -> 2H20(l) + 2e-

Not sure how to differentiate between these two.
The answers say
"Since the electrolyte is alkaline, the oxidation half-equation must contain OH-(aq) ions"
Why is this the case?
The electrolyte is KOH which is the same for all simple galvanic cells... most of which don't involve OH-(aq) as a reactant?
Am i missing something here?
thanks!

[WhoTookMyUsername]

Why can't it happen ? (i'm not great at chem )