Question: I just read that physical changes are temporary and reversible while chemical changes are permanent and irreversible. If that is the case, why are some chemical reactions reversible. Does it mean that chemical changes are reversible?

Answer: 
I am actually pretty old to this subject and still I cannot really answer, because **the boundary between physical changes and chemical reactions is indistinct.** Essentially anything that involves rearrangement at an atomic or molecular level, even something as seemingly straightforward as melting ice or dissolving sugar into water, has characteristics of a chemical reaction.

Let us compare the melting of ice with something that is obviously a chemical reaction. For the latter, we choose the reaction of elemental carbon at high temperature with carbon dioxide gas, forming carbon monoxide:

$\text{C(s) + CO}\_2\text{(g)}\overset {\Delta}{\to} 2\text{CO(g)}$

First off, both processes are advanced by heating the material. True, carbon requires a higher temperature to react at an appreciable rate with carbon dioxide than ice requires to melt, but this amounts only to a difference in degree rather than a difference in kind of process. Moreover, and more to the point, both the "physical change" of melting ice and the "chemical reaction" of carbon with carbon dioxide can be reversed upon cooling; in the latter case it can lead to a real industrial problem of furnace parts being covered with soot in the *cooler* parts of the furnace.

One might suppose that we could differentiate the above processes hecause the reaction of carbon with carbon dioxide surely involves the breaking and making of bonds. True, the bonds in carbon monoxide are arranged quite differently from those in the carbon and carbon dioxide from which it can be made. But the same holds true with melting ice, which involves the breaking of hydrogen bonds. The [molecular orbital description of hydrogen bonds[1]](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4764947/#!po=1.11111) identifies this hydrogen bonding as a form of (delocalized) covalent bonding -- weaker bonds than those rearranged when carbon and carbon dioxide are heated in a furnace, but again there is only a difference in degree and not in the fundamental type of process.

So there is no clear boundary between physical and chemical changes. Physical changes can be reversible, and so can chemical reactions. Chemical reactions may be essentially irreversible, and (as I look at the scar permanently left on my arm after a long-ago surgery) so can physical changes.

**Reference**

1. Bo Wang, Wanrun Jiang, Xin Dai, Yang Gao, Zhigang Wang, and Rui-Qin Zhangb (2016). "Molecular orbital analysis of the hydrogen bonded water dimer". *Sci Rep.* **6**: 22099. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4764947/#!po=1.11111>
All chemical reactions are reversible. But the back reaction may be extremely improbable. For exemple the combustion of hydrocarbons produces $\ce{CO2}$ and $\ce{H2O}$. But if you mix and heat a mixture of these two gases, you will never even obtain one molecule of any hydrocarbon by the back reaction, because the equilibrium constant is rather huge. The reaction seems irreversible.