[s.aley]

no

[Pride]

well, have you been doing bond enthalpies?

when carbon is oxidised, the O-O bond in O2 breaks, taking energy to break. Then the two C-O bonds are reformed in the CO2 and this releases energy.

The reaction is exothermic, so you see this means that the bonds reformed are stronger than the bond broken. If you're doing OCR A I know you'll have been learning that

[charco]

(Original post by s.aley)
when a bond is made energy is released, but where was that energy when the two atoms were still dissasociated?
energy cant be created or destroyed, in what form was it prior to the bond being formed?

The heat energy is produced from chemical potential energy. The chemical potential energy can be thought of as being a function of the nature of a substance and its position in the universe relative to everything else.

The chemical potential energy cannot be determined, but changes in heat energy can be ascribed to similar (but opposite) changes in chemical potential energy.

Check this out

[qiaoyu.he]

(Original post by s.aley)
No no,thanks for answer.

What i wanted to know was why are some bond enthalpies higher than others? as in how is energy released from forming bonds? what happens in terms of the energy of electrons or somthing along those lines

is it to do with the distance between the charged particles? what does it mean for the electrons to be in a lower energy state? Does being more energetically favourable mean electrons being closer to the nucleus or what?

thats what i wasnt so sure about.

when a bond is made energy is released, but where was that energy when the two atoms were still dissasociated?
energy cant be created or destroyed, in what form was it prior to the bond being formed?

please and thanks

These questions are quite deep chemistry/physics and it is difficult to give a full answer without going into lots of maths. To understand this, you need to treat electrons as wavefunctions (i.e. waves) and particles.

Basically, there is an electrostatic force of attraction between the protons and the electrons. You would expect the electrons to simply fall into the nucleus, but due to their velocity, they maintain an orbit (sort of like planets around the sun, but remember, the electrons are waves). Due to quantum mechanical considerations, the electron 'orbits' form different shapes, the s, p, d, f sub-shell shapes. The shapes do not have rigid boundaries, but form smooth gradients that extend throughout the universe with high density areas and low density areas. The electron wavefunction is more present in the high density areas and less present in the low density areas. The 1s orbital, for example, is a sphere with the electron wavefunction more present in the nucleus and less present the further you go from the nucleus.

Consider 2 hydrogen atoms bonding. They both have 1s1 electronic configurations and their electrons have a spherical wavefunction. When the 2 orbitals come close together, they will tend to overlap. Due to the particular properties of wavefunctions, when overlapping occurs, you simply add together the wavefunctions, to form an hourglass shaped orbital so the 2 electrons will be more present in-between the hydrogen nuclei. This increases attraction between the nuclei and electrons and so the interaction is more favourable.

As for where the energy is before a bonding interaction, you need to consider the principle of conservation of energy and mass. You stated that energy is conserved, but that isn't strictly true. The sum of energy and mass is always conserved where energy and mass can be considered the same thing. Einstein's formula, E=mc^2 tells us that energy and mass are the same thing and gives us the conversion formula. So energy as heat is released after a bonding interaction, but the sum of the energy and mass of the 2 atoms remains constant. Therefore, after a bonding interaction, the mass of the molecule produced is less than the sum of the masses of the component atoms. The energy was stores as mass. This isn't to say that any part of the atoms have disappeared, just that the wavefunction overlap has resulted in the loss of total mass of the system.

If you didn't get any of that, don't worry, no one else in the world does either.

[qiaoyu.he]

(Original post by s.aley)
infact this kind of response is exactly what i was looking for. all this that your saying is what i've been reading online today. And i get a good fraction of what your saying, but theres plenty of things that im looking up which is leading me to look up more and more things. bit tricky to find a good order to learn them all.

when i posted the question i had physics in mind, your exactly right about the chemistry/physics thing, it is a sort of a border between the two. especially thermodynamics etc.

thanks for your response

I'm glad I could be of help. When I was in 6th form, I remember wanting to know exactly this type of thing as well, but my teachers refused to teach me because either they didn't understand it, or they just couldn't be bothered. I feel students should be a bit more free to explore their subject with teachers rather than being bound by the curriculum. Do you mind me asking what year you're in and what subjects you're doing?

[illusionz]

(Original post by qiaoyu.he)
I'm glad I could be of help. When I was in 6th form, I remember wanting to know exactly this type of thing as well, but my teachers refused to teach me because either they didn't understand it, or they just couldn't be bothered. I feel students should be a bit more free to explore their subject with teachers rather than being bound by the curriculum. Do you mind me asking what year you're in and what subjects you're doing?

Edit: never mind. Stupid question easily solved by a quick google search

As you seem to know a fair bit about this, just wondering if you were able to explain why the zero point energy of an X-D bond is lower than that of an X-H one. I know it's because D is heavier but that's all the detail I've been into seeing as I've avoided theoretical chemistry like the plague and only covered it in terms of kinetic isotope effects.

[PowerPuff]

OR. A simple answer, dont think of it as the oxidation of carbon but the combustion of carbon (burning in excess oxygen) which is always exothermic

[qiaoyu.he]

(Original post by illusionz)
Edit: never mind. Stupid question easily solved by a quick google search

As you seem to know a fair bit about this, just wondering if you were able to explain why the zero point energy of an X-D bond is lower than that of an X-H one. I know it's because D is heavier but that's all the detail I've been into seeing as I've avoided theoretical chemistry like the plague and only covered it in terms of kinetic isotope effects.

fufufu, no. 1A Cambridge BioNatSci. Not even a chemist or physicist, but with an interest in theoretical physics.

What is zero point energy? If you find out an answer, I'd love to know.