They throw it away.
If you light the yahrzeit candle before it's time to light the Hanukkah-menorah, you may light the yahrzeit candle first. Otherwise, once it's past sunset, you should wait until about 20 minutes after sunset, light the Hanukkah-menorah, and afterwards light the yahrzeit candle.
Yes.
It's actually spelled yahrzeit candle. It is a candle lit in memory of the dead in the Jewish religion.
Yes, I think so.
the products of a burning candle are water vapor and carbon dioxide
Burning a candle is a chemical change, as is burning anything.
The Yahrzeit does not come straight after the death, but on the anniversary of the death. Therefore, if you light a candle - even one intended for the Yahrzeit that burns for 24 hours - on the evening after the death has occurred, it is not technically a Yahrzeit candle. I can't see that there would be anything halakhically (by Jewish law) wrong with doing so, but I would most definitely urge you to check this with a rabbi and don't just take my word for it. There are several online "ask the rabbi" services who will be able to help you with this - I'd recommend the one at www.chabad.org as they've never let me down yet and will send a personal reply usually within a day or two.
Candle wax is the fuel a candle uses to keep burning. So, I guess the effect of the wax is the candle keeps burning.
what name is given to a process such as burning a candle?
A burning candle produces thermal energy and light.
a burning candle is a light source due to the fire.
I think a burning and unattending candle is not safe because little kids can burn on the candle.