VCE Chemistry Question Thread

[Splash-Tackle-Flail]

Your theory sort of makes sense tbh.. But the answer adds them together not minus. Any thoughts about why? Cheers

That's weird imo. The reverse reaction is exothermic because the original is endothermic, so the exothermic reaction (for this situation) should have a lower activation energy than the endothermic one (so shouldn't be able to be above 167), that is, unless I've missed something here.

[cosine]

That's weird imo. The reverse reaction is exothermic because the original is endothermic, so the exothermic reaction (for this situation) should have a lower activation energy than the endothermic one (so shouldn't be able to be above 167), that is, unless I've missed something here.

How come you say that just because the forward reaction is endothermic, the backward one must be exothermic? Can you explain?

[Splash-Tackle-Flail]

How come you say that just because the forward reaction is endothermic, the backward one must be exothermic? Can you explain?

Well endothermic means the enthalpy (thermal energy) in the products is higher than the enthalpy in the reactants. So in the reverse reaction the products and reactants are switched, meaning the enthalpy in the products is not lower than the enthalpy in the reactants (see attached)

[cosine]

Well endothermic means the enthalpy (thermal energy) in the products is higher than the enthalpy in the reactants. So in the reverse reaction the products and reactants are switched, meaning the enthalpy in the products is not lower than the enthalpy in the reactants (see attached)

Ah yes, I see. But so what about the original question. Any idea as of why they add the two figures?

[paper-back]

Ah yes, I see. But so what about the original question. Any idea as of why they add the two figures?

Just adding my $0.02, but I think splash-tackle-flail is correct in subtracting the 2 figures... unless I'm also reading the question incorrectly

[Splash-Tackle-Flail]

Ah yes, I see. But so what about the original question. Any idea as of why they add the two figures?

If the forward reaction was exothermic, with the activation energy of 167, and heat of reaction as -28   then to find the activation energy of the reverse (endothermic) you'd add the two, but the question said endothermic...

[Alter]

Hi all, I've received instructions for a practical component of a SAC I have next week, but I'm having trouble understanding one of the parts of it.

In one of the stages we have to create a hydrogen-oxygen fuel cell with potassium hydroxide solution. It says we that after the electrode is filled and inverted, surface tension should hold the potassium hydroxide in the inverted electrode. However, it doesn't really say what the electrodes are made out of? I'm quite lost and not sure what's going on with inverted electrodes. I don't believe I've seen a diagram of this process before.

Thanks in advance.

[Splash-Tackle-Flail]

See picture

Oh whoops, I've always thought activation energy was the amount of energy to break the bonds, not the original amount of chemical energy? Sorry cosine, I've probably misled you down the wrong path then!

[cosine]

Oh whoops, I've always thought activation energy was the amount of energy to break the bonds, not the original amount of chemical energy? Sorry cosine, I've probably misled you down the wrong path then!

Wait what? I thought activation energy was the energy required to break the chemical bonds within reactant molecules? How can activation energy be the original amount of chemical energy? I can't see BakedDwarf's image

[Splash-Tackle-Flail]

Wait what? I thought activation energy was the energy required to break the chemical bonds within reactant molecules? How can activation energy be the original amount of chemical energy? I can't see BakedDwarf's image

Ok so I googled the definition to be sure, and yes activation energy is the minimum energy required to break the chemical bonds within reactant molecules, so not too sure about BakedDwarf's image. I'd stick with subtracting the two- so 139kj mol, at least until euler or someone can confirm/refute.

Edit: added "minimum" to please VCaa

[keltingmeith]

Ok so I googled the definition to be sure, and yes activation energy is the minimum energy required to break the chemical bonds within reactant molecules, so not too sure about BakedDwarf's image. I'd stick with subtracting the two- so 139kj mol, at least until euler or someone can confirm/refute.

Edit: added "minimum" to please VCaa

Dat VCAA pleasing.

But yeah, solid logic. The thing with unit 4, you *can* get away with formula spamming (which is what the solutions tried). But, doing things as simple as drawing an energy profile/the cell/whatever process is happening can make a massive difference, means you're less likely to pick the wrong formula and can get a feel for what's actually happening. Remember, chemistry is largely a practical science - you're not going to be given a question about something that doesn't intrinsically exist.

[cosine]

Dat VCAA pleasing.

But yeah, solid logic. The thing with unit 4, you *can* get away with formula spamming (which is what the solutions tried). But, doing things as simple as drawing an energy profile/the cell/whatever process is happening can make a massive difference, means you're less likely to pick the wrong formula and can get a feel for what's actually happening. Remember, chemistry is largely a practical science - you're not going to be given a question about something that doesn't intrinsically exist.

Is for my original question, why do we minus the two energies?

[RazzMeTazz]

Since Le Chatelier's principle says that the reaction system will only partially oppose the physical change, does this apply to temperature as well?

So for this equilibrium reaction:

N2O4(g) <==> 2NO2(g); endothermic

If you decreased the temperature of the reaction system, the equilibrium position would shift to the left (as the backward reaction is exothermic), but would it be correct to say that the final temperature would always still be lower than the initial temperature, as the system can only partially restore the temperature change?

Thanks

[I am a unicorn]

Hello

Does the size of the electrode in a galvanic/electrolytic cell influence the rate of reaction?

Thank you!

[Redoxify]

What measure can be used to determine rate of reaction?