[Shlep]

“Experiment 31.—Put into a small ignition-tube a mixture of 4 or 5 g. of powdered copper oxide (CuO), with half its bulk of powdered charcoal. Heat strongly for ten or fifteen minutes. Examine the contents for metallic copper. With which element of CuO has C united? The reaction may be written: Cu0 + C = CO + Cu. Complete and explain.”

Excerpt From: Rufus Phillips Williams. “An Introduction to Chemical Science.” iBooks.
This material may be protected by copyright."

I simply wonder why CO2 isn't produced, is that a matter of stoichiometry and exact heat input not expected of a student?

[Arkcon]

It is dependent on temperature, as given here: http://en.wikipedia.org/wiki/Carbon_monoxide#Production  Also, if there isn't an excess of oxygen, CO is favored.  When you pack something onto the bottom of a tube, and heat it with one end open to the air, and give off some gas, then you drive the air with its oxygen out, and you only have what the mixture brings with it.  You might expect CO2 if you roast the powder in an open pan, as an example.

[Shlep]

I guess my point is why not  2CuO + C = Cu + Cu + CO2

The carbon isn't strong enough to react the CuO unless it has 2 available bonds?

The open air is hot CO bonding to O from the air and not related if the copper reaction is the focus / reason for spending energy yes?

[Arkcon]

Yes.  That wikipedia article links to another wikipedia article (and you could have done this yourself): http://en.wikipedia.org/wiki/Boudouard_reaction  that explicitly states that:

While formation enthalpy of CO2 is higher than that of CO, the formation entropy is much lower. Consequently, according to the Ellingham diagram, the overall free energy change of formation of CO2 by oxidation of carbon is almost constant and indifferent of the temperature, while the free energy change of formation of CO is a decreasing line. These two lines meet at 700℃, so the Boudouard reaction implies that on lower temperatures the equilibrium is on the exothermic carbon dioxide side and on higher temperatures the endothermic formation of carbon monoxide is the dominant reaction.

So you see, at higher temperatures, you are more likely to get CO than CO₂, despite entropy, and CO₂ you might make become CO.