thefatone
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2 requirement for a reaction to occur between 2 gases?

Peroxidation
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Peroxidation
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Well high temperatures are good for speeding things up, high pressures work well too. In the case of high temperatures, the reactants have much more kinetic energy so more of them have an energy higher than the activation energy. They also collide more often due to the higher speeds so the number of reactions occurring per unit time increases. With higher pressure there's more reactants per unit volume so collisions between the reactants are more frequent. You can also use a catalyst.

You've got to be careful with equilibrium reactions though. With these temperature and pressure also affect the yield so you have to compromise between rate and yield. You can also use a catalyst here too, if it's a solid it won't affect the pressure of the system and will speed up the rate of reaction.
Sorry for the late reply, I've been asleep.
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Pigster
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You understood the question?

There was even a question?
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thefatone
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(Original post by Peroxidation)
Well high temperatures are good for speeding things up, high pressures work well too. In the case of high temperatures, the reactants have much more kinetic energy so more of them have an energy higher than the activation energy. They also collide more often due to the higher speeds so the number of reactions occurring per unit time increases. With higher pressure there's more reactants per unit volume so collisions between the reactants are more frequent. You can also use a catalyst.

You've got to be careful with equilibrium reactions though. With these temperature and pressure also affect the yield so you have to compromise between rate and yield. You can also use a catalyst here too, if it's a solid it won't affect the pressure of the system and will speed up the rate of reaction.
Sorry for the late reply, I've been asleep.
ok thanks so much

(Original post by Pigster)
You understood the question?

There was even a question?
yes yes an here's another one

Is temperature of the mixture being raised or the concentration of the reagents better at increasing the rate of reaction?
another one i need help with is defining what mean bond enthalpy is
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Pigster
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Your Q cannot be answered, how large a change in T or conc?

Mean bond enthalpy can easily be looked up on Google/Wikipedia. You'll learn this sort of thing much better if you have to do a bit of research yourself than for someone to just give you answers.
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Peroxidation
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(Original post by thefatone)
ok thanks so much



yes yes an here's another one

Is temperature of the mixture being raised or the concentration of the reagents better at increasing the rate of reaction?
another one i need help with is defining what mean bond enthalpy is
Both would increase the rate, temperature does what I described above and increasing the concentration works in the same way as increasing the pressure. You increase the probability of the reactants colliding at the right orientations with the right energies because there's more of them colliding per unit time. It's hard to say which one works best though, there's so many factors that affect the rate of reaction which also affect each other that in the end it's hard to see what's doing what unless you keep them all constant except for one and then measure the rate. Like, high concentration and/or pressure is all well and good but if the reactants don't have enough energy it's not going to help much, so you'd need to raise the temperature as well depending on the activation energy value.

As for the mean bond enthalpy, you get the same type of bond/functional group occurring in all sorts of different molecules/lattices. But what's attached to other parts of the structure has a big effect on how each functional group behaves and the bond energies in the molecule. It's probably easier if I give an example...

Lets take for instance hydrogen peroxide and the peroxodisulfate ion. The bond responsible for most of their chemistry is the peroxide bond, O-O. As you can imagine, oxygen hates doing this and the bond is really unstable but that's cool because it makes peroxides great oxidising agents. If you look at their standard electrode potentials, you'll notice that peroxodisulfate is stronger than hydrogen peroxide despite the peroxide bond in both giving rise to their oxidising powers. You can see why if you take a gander at their structures. In peroxodisulfate you've got 4 oxygen atoms per sulfur atom and as you know oxygen's a real electron hog so you end up getting electrons throughout the molecule drawn towards the two ends of the molecule. The peroxide bond's in the center so it's like the bond is being yanked on both ends at once in terms of the forces acting on it. As you can imagine the bond's put under quite a bit of stress. This drastically lowers the bond's stability and hence the bond enthalpy of the peroxide bond in peroxodisulphate is lower than that of the peroxide bond in hydrogen peroxide.

Image

If you add up all of these different bond enthalpies for a particular bond and then find the average you'll get the mean bond enthalpy for that bond. But because of things like the inductive effect which I described above bond enthalpies are never used for anything more than an approximate expected value since your actual bond enthalpy could be quite different from the mean. This is especially bad if you have electronegative or electropositive atoms complicating things in the molecule.

I suppose the definition would be something along the lines of "the average enthalpy change when 1 mole of a bond is broken." The values given are always positive so never put the energy released when 1 mole of those bonds are formed (even though it's the same value), always talk about it in terms of breaking them.

Sorry for the long post, I put the extra info in there because it often helps if you have an understanding of the factors affecting bond enthalpies. That way if examiners throw you a curve ball you've got a better understanding on the concept so you'll be in a better position to tackle it.
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Bigbosshead
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With the question specifying two gases, I would believe that being in a closed system will help
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