Hi I was wondering when to apply the molar volume for gases where you can determine the volume of a gas in a reaction given the stoichiometric coefficients of every reactant and product.

I am not sure if the following is correct, I know how I allocate A, B, C and D as the different states of matter may be wrong in terms of reaction but they are examples. Please correct me if I'm wrong.

Say

A+B->C+D

Scenario 1: I know if A, B, C, D are gases, I can use the molar volume to determine the volume of any of their gases.

Scenario 2: If A is a solid, B is a liquid and C and D are gases, if I want to find out how much A is needed to form a particular quantity of D ( maybe 3g ), then since A is not a gas, I will have to use the molar calculation method, by finding no of moles and equating then multiplying by the molar mass of A etc. I cannot use the molar volume method, simply because not all of the elements I am 'comparing' are not in gaseous state.

Scenario 3: If A is a solid, B is a gas and C is a liquid and D is a gas, if I want to find out how much B is needed to form a particular quantity of D ( maybe 3g ), then can I use the molar volume method? I'm not sure as the reaction is not all gases..

I really need to understand this.

Thank you so much!

Thanks in advance,

J