cuando un gas que se encuentra a 20°c se calienta hasta lo 40 °c sin que varié su presión. su volumen se duplica

I’m not sure what your trying to say here.. can you clarify again?

Answer; carbon monoxide (co);

Answerδh > 0explanationc₆h₆  (s)  → c₆h₆ (l)if you are changing it from a solid to a liquid, you are pretty much melting the solid. this requires heat energy. therefore, the reaction is endothermic (takes in energy); the system enthalpy increases as the reaction proceeds: δh > 0.