1)Can a reaction have proton transfer?
proton transfer reactions would refer to acid-base reaction. a bronsted acid is defined as a proton donor and a bronsted base is proton acceptor.
2)When writing half reactions, do you perserve the subscripts in the compound or write as a coefficient?
eg) 2Al + 3Cl2->2AlCl3
would the half rxn of Cl be 3e+3Cl2->Cl3(-) or 3e+3Cl2->3Cl(-)?
Yes, you preserve the subscripts, unless it's more than meets the eye. eg. HCl(aq) isn't hydrogen chloride molecule exist a matrix of water molecules, but actually H+
ions. When one writes the half reaction involving HCl(aq), he will quote one of the ions.
BTW the correct half equation for chlorine is:
6e + 3Cl2
(g) -> 6Cl-
3)Why is the change in oxidation number same as the electron transferred?
oxidation number essentially refers to number of electron "gain" or "lost" when an atom forms covalent bond. eg. the oxidation number of carbon in O=C=O is +4. it uses 4 electrons to bond with oxygen. Being more electronegative, the electrons from oxygen tend to be more attracted to the oxygen nucleus than that of carbon, hence carbon "loses" 4 electrons, thus its oxidation number is +4.
4)For oxidation numbers, do we assume that covalent compounds transfer electrons?
5)What is a non-spontaneous reaction?
non-spontaneous reactions are chemical reactions whose product is energetically higher than the reactants. such chemical reactions are also endothermic