If 0.5000grams of barium carbonate was reacted with 25.0mLs of 0.15M nitric acid and the gas then collected in 100mL flask at 77°C, what is the gas pressure in the flask?

Answer 1

I assume the vapor pressure of H2O at 77 C is ignored as well as the volume occupied by the liquid HNO3.
This a limiting reagent problem coupled to a gas law PV = nRT problem.
BaCO3 + 2HNO3 ==> Ba(NO3)2 + CO2 + H2O
mols BaCO3 = grams/molar mass = ?
mols HNO3 = M x L = ?

Convert mols BaCO3 to mols CO2 using the coefficients in the balanced equation.
Do the same for mols HNO3 to mols CO2.
It is likely that the values for mols CO2 will not agree which means one of them is wrong. The correct value in limiting reagent problems is ALWAYS the smaller value and the reagent providing that number is the limiting reagent.
Then use PV = nRT and the smaller mols to obtain pressure.