Nitroglycerine decomposes according the the equation: 4C3H5(NO3)3 - 12 CO2 + 10 H2O +6N2 + O2. 15.0 g of nitroglycerine is placed in a 500 ml flask at 25.0 C. The vapor pressure of water at this temperature is 23.8 mmhg. Find the total pressure in the flask after the reaction is complete, and determine the mole fraction of carbon dioxide. So I must find how many moles of each gas and h2o are formed? Do I add only the gases and use them in pv=nrt? And then substract the vapor pressure of water from the final P?

Question

Nitroglycerine decomposes according the the equation: 4C3H5(NO3)3 -> 12 CO2 + 10 H2O +6N2 + O2.  15.0 g of nitroglycerine is placed in a 500 ml flask at 25.0 C.  The vapor pressure of water at this temperature is 23.8 mmhg.  Find the total pressure in the flask after the reaction is complete, and determine the mole fraction of carbon dioxide.  So I must find how many moles of each gas and h2o are formed?   Do I add only the gases and use them in pv=nrt? And then substract the vapor pressure of water from the final P?

DrBob222 · Answer

1. Yes, find the moles of each MATERIAL and i would include water.
2. Add the moles of the gases together, then add in 23.8 mm Hg for the H2O vapor pressure. From the problem I assume the temperature is to stay at 25 C and we assume no heat is given off in the explosion. If heat is given off then the water will be transformed to a gas and I would add in the moles water vapor, also, and forget about the 23.8.
3. Use the sum of the moles and PV = nRT to calculate total pressure.

Ben · Answer

Thank you very much for your time.