Re: What is the life span of a atom ?

I assume that you are referring to radioactive decay.

1. Radioactive decay occurs through three mechanisms, alpha particles, beta particles and gamma radiation. Gamma radiations are electromagnetic radiations and have no mass. Alpha particles are helium nuclei and beta particles are high energy electrons. Of course, they have to come from somewhere. That somewhere is the existing atoms of the radioactive matter. but when an atom loses it's electrons or parts of it's nucleus, it transmutes itself into another atom. This is called a nuclear reaction.

If we were concerned with the life span of the original atom, then we could define it as the time from creation to transmutation. Supposing now that a mass of radioactive matter has initially 100 atoms, how do you determine which atom will decay first? You will realise that it is an impossible question and can be answered only in probabilistic terms. The point I am trying to get at is that your primary question is probably not the appropriate one to ask. It's a different story, however, if we ask what is the life span of a sample of radioactive matter.

Radioactivity is what we model as a first order process - the rate of decay is proportional to the amount at present. Therefore, it will decay faster at the beginning when there is more mass than later. These processes are characterised by a term called half life which is the time for half the initial amount to decay, and that you can take to be a representative lifespan of the matter.

2. Why not? When carbon monoxide comes in contact with air, it combines with oxygen to form carbon dioxide. The carbon atoms are the same.

Finally let me just mention that heat is a form of energy in transit. It has no mass and hence it does not contain atoms.

I hope I have answered to your satisfaction. let me give you an interesting link.