Question

What does it mean for example: 100% of methane and oxygen entering are consumed by reactions 1 and 2..

Or another example... 95% of hydrogen entering is consumed...

Answer 1

Answer:

It simply means the all methane and oxygen entering the system is consumed by the reactions.

For example: (Assume reaction is very fast, don't get confused with time).

• If complete combustion of methane ( CH₄ + 2O₂ CO₂ + 2H₂O ) takes place in a reactor and if 25 mol/s of methane and 50 mol/s are fed to the system. From the above combustion reaction 2 mol of oxygen react with 1 mol of methane. Therefore, 50 mol of oxygen react with 25 mol of methane i.e., all methane and oxygen entering the reactor is 100 % consumed leaving nothing in the product stream.
• Now, consider the case when 30 mol/s of methane and 80 mol/s of oxygen is fed to the reactor and assume that complete combustion of methane takes place. From the stiochiometry of the above reaction, 1 mol of methane reacts with 2 moles of oxygen. Therefore, 30 mol of methane will react with 60 mol of oxygen. 20 mol of oxygen are left unreacted i.e., 100 % of methane entering the reactor and [{60/80} x100] 75 % of oxygen entering the reactor is consumed by the reaction.

If the reactant is comsumed fully (100%) the reactant can not be in the product stream. If it is consumed partially say 90 % then10 % of unreacted reactant will in the product stream.

It is not necessary that the reactants will be consumed fully if we fed reactants in the ratio same as of their stichiometric ratio. There may be several causes like if the rate of reaction is larger than the rate at which reactants are fed to the system, partial combustion, undisered reaction which may use reactants in different stichiometric ratios etc. I hope you may be aware of the terms like limiting reagent and excess reagent.

If you have still any douby feel free to ask me.