When you melt a covalent network, you break intramolecular covalent bonds, is that not a chemical change?
Also, is ionisation a chemical or physical change?
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1$\begingroup$ This is more or less pointless categorisation and only useful for passing exams IMO. Still if you heat elements and the process is reversible - you can solidify melt to get the same thing or even ionise vapor and get the same thing after cooling, that is considered "physical". $\endgroup$– MithoronCommented Aug 20, 2016 at 15:20
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A chemical change is defined as when your substance reacts with another substance to form some products, or decomposition into other products. In a chemical change, there will be formation of new chemicals that are different in terms of chemical formula.
Thus, breaking of intramolecular bonds will not be a chemical change in the case of C-C bonds in diamond/graphite, because there is no formation of new chemical substances with an alternative formula. Similarly, ionization (without formation of complex ions) would be physical change
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$\begingroup$ Uh, there are no molecules in graphite. Or diamond. $\endgroup$– M.A.R.Commented Aug 20, 2016 at 7:32
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$\begingroup$ @DEAD Intramolecular forces refers to covalent/ionic/metallic bonds between the atoms that make up a molecule. In this case I raised the example of diamond/graphite because it is a covalent network and the bonds are considered intramolecular $\endgroup$– LSDCommented Aug 20, 2016 at 7:41
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$\begingroup$ Your statement that breaking intramolecular forces is not a chemical change is blatantly wrong. $\endgroup$– M.A.R.Commented Aug 20, 2016 at 9:01
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$\begingroup$ A chemical change is defined by the formation of new chemicals from the original substance via a chemical reaction. The context in this question is strictly restricted to breaking of bonds of a networked structure (i.e. macromolecular covalent structure), as the breaking of intramolecular bonds in a simple covalent structure (e.g. H-Cl bond) would be trivially a chemical change, due to formation of other chemicals with a different formula. I argue my case from the fact that there is no formation of new chemical products with a chemical formula different from the original substance. $\endgroup$– LSDCommented Aug 20, 2016 at 9:35
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$\begingroup$ I respectfully disagree. The products necessarily do not have a different chemical formula than that of the reactants. Could you provide a source on your claims? $\endgroup$– M.A.R.Commented Aug 20, 2016 at 9:42