Ethyne (c2 h2 (g), mc032-1.jpghf = 226.77 kj/mol) undergoes complete combustion in the presence of oxygen to produce carbon dioxide (co2 (g), mc032-2.jpghf = –393.5 kj/mol ) and water (h2 o(g), mc032-3.jpghf = –241.82 kj/mol) according to the equation below.

mc032-4.jpg

what is the enthalpy of combustion (per mole) of c2 h2 (g)?
–2511.2 kj/mol
–1255.6 kj/mol
–862.1 kj/mol
–431.0 kj/mol

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"