# Does wood have only one phase?

I was reading the Knight textbook, which stated in Chapter 16.1 (A Macroscopic Description of Matter) the following:

"The notion of three distinct phases is less useful for more complex systems. A piece of wood is solid, but liquid wood and gaseous wood don’t exist."

Can someone explain to me what is meant by "more complex" and its relationship to phase transition? That is, why can't one describe a phase transition for a piece of burning wood even though, as it appears to me, that it transitions into a gas (i.e. sublimation)?

• The temperature at which wood melts is much higher than the temperature at which it burns. Therefore, it is not possible to melt wood (at least when it is surrounded by oxygen). Jan 13, 2014 at 22:00
• Another issue is that 'wood' is from a physics perspective not a single material. The resin contained in wood for example can be solid, liquid or in the gas phase. Lignin is a large molecule that will break apart before melting, etc. Jan 13, 2014 at 22:06
• @Hunter: can you explain more why wood melts at a much higher temperature than when it burns. Thanks. Jan 13, 2014 at 22:07
• thenakedscientists.com/forum/index.php?topic=7504.0 Jan 13, 2014 at 22:13
• @Alexander: thanks, this was very useful to my understanding and makes it very clear now! Jan 13, 2014 at 22:24

It appears that wood is complex in its chemical state as it contains components of both liquid and solid form. Also when you burn wood many chemical reactions take place, primarily the converion of its carbon content to coke as well as production of $CO_2$, remember that it both goes in smoke and stays behind as ash, this is not a conventional phase transition as there is no clear phase change, it is much more of a chemical reaction with products in different state.