6-6 Solve stoichiometry problems involving gases

6-6-1. A piece of Mg ribbon is reacted with hydrochloric acid. If 224 mL of hydrogen gas is produced at 25.0oC, 1.00 atm, how much HCl was consumed? The reaction is:
Mg(s) + 2 HCl(aq) == MgCl2(aq) + H2(g)




6-6-2. Consider the combustion of urea:
2 CO(NH2)2 (s) + 3 O2(g) == 2 CO2(g) + 2 N2(g) + 4 H2O(l)
Suppose 3.00 g of urea were burned in excess oxygen in a fixed-volume 1.00-L sealed container that initially contained 2.00 atm of O2 at 298K. Estimate the final pressure in the container at
298K?



6-6-3. Consider the hypothetical reaction:
2 A(g) == B(g) + 3 C(g)
Suppose a fixed-volume container initially contains 2.00 mol of pure A(g) at a pressure of 0.500 atm. Hours later, the pressure, at the same temperature, is found to be 0.800 atm. How many moles of B(g) are present in the final mixture?