Because you’re assuming only the identified products are made, and you aren’t destroying or creating any of the atoms - you’re just rearranging the configuration. You have CO and H2O. If you form CO2, you have 2 Hydrogens left, so you get H2. That accounts for all of the atoms.

2 hours ago, HbWhi5F said:

Why is products assumed to formed in equal amounts ?

Because that is the stoichiometry of the chemical reaction.

@KJW thanks

I don't usually answer this OP since they refuse to enter discussion.

However I would point out for the benefit of others who may read this that

There is no such thing as a forward equilibrium constant or a backward equilibrium constant.

That would be a direct contradiction of terms.

As @sethoflagos has already pointed out at equilibrium the reaction is not proceedijg; It is going nowhere.

This follows from the definition of equilibrium.

As shown in this thread there are two competing reactions, a forward reaction and a reverse reaction, both of which are proceeding.

Each of these have their own reaction rate constants, which are not and cannot be equilibrium constants, by definition.

On 9/13/2025 at 6:43 PM, KJW said:

Because that is the stoichiometry of the chemical reaction.

Yes agreed the reaction rate constants do not play a part in the calculation., even though the equilibrium constant is their ratio, and therefore a pure number.

Thanks also to @swansont in the other thread for referencing the full test of the source material, which I agree is clunsily drafted.

Just to clarify in case there's any doubt, @swansont 's answer and @KJW 's are pointing to one and the same principle: Atoms are conserved in chemical reactions.

Stoichiometry is nothing but a book-keeping tool for that experimental fact.

41 minutes ago, joigus said:

Just to clarify in case there's any doubt, @swansont 's answer and @KJW 's are pointing to one and the same principle: Atoms are conserved in chemical reactions.

Stoichiometry is nothing but a book-keeping tool for that experimental fact.

It's a little more than that as it also includes charge conservation, which you need sometimes to gather the right number of equations to complete the set for solving.

14 minutes ago, studiot said:

It's a little more than that as it also includes charge conservation, which you need sometimes to gather the right number of equations to complete the set for solving.

When you contemplate the red-ox aspect of chemistry, right. Then you have to account for charge conservation as well in the partial ionic reactions. It's often a clue when you don't know all the atomic/molecular participants in detail.

Thank you for pointing it out.

Stoichiometric balancing is about number of atoms.

red-ox balancing is about electron, proton, and sometimes hydroxide-ion numbers, depending on how acidic the medium is.

It's all about protons, neutrons, and electrons. Nothing else. There are no nuclear re-arrangements.

I was somehow feeling the student is not busy with balancing electrons yet.

There are such things as non stochiometric compounds,

https://en.wikipedia.org/wiki/Non-stoichiometric_compound

These are still made of atoms and or other particles.

On 9/17/2025 at 2:21 PM, studiot said:

There are such things as non stochiometric compounds,

https://en.wikipedia.org/wiki/Non-stoichiometric_compound

These are still made of atoms and or other particles.

Thank you, Studiot. That's very good to know.