(nh₄)₂CO₃(s) ? 2NH₃(g) + CO₂(g) + H₂O(l) {balanced}
In an experiment, a sample of solid ammonium carbonate was allowed to decompose under STP conditions. The combined gas phase decomposition products had a total volume of 6.8L. What mass of starting material decomposed?

A. 5.6 g
B. 11.2 g
C. 16.8 g
D. 22.4 g