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?
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.
Thank you very much for your time.
To find the total pressure in the flask after the reaction is complete, as well as the mole fraction of carbon dioxide, you need to determine the number of moles of each gas and water formed during the reaction.
Let's start by finding the number of moles of nitroglycerine:
Given:
Mass of nitroglycerine = 15.0 g
Molar mass of nitroglycerine = 227.09 g/mol
Number of moles of nitroglycerine = mass/molar mass
Number of moles of nitroglycerine = 15.0 g / 227.09 g/mol
Next, we need to determine the number of moles of each product formed in the reaction. By examining the balanced chemical equation, we can see the stoichiometric ratios between the reactants and the products.
From the balanced equation, we can determine the following stoichiometric ratios:
1 mol nitroglycerine -> 12 mol CO2
1 mol nitroglycerine -> 10 mol H2O
1 mol nitroglycerine -> 6 mol N2
1 mol nitroglycerine -> 1 mol O2
Multiply the number of moles of nitroglycerine by each stoichiometric ratio to find the moles of each product:
Moles of CO2 = (Number of moles of nitroglycerine) x (12 mol CO2/1 mol nitroglycerine)
Moles of H2O = (Number of moles of nitroglycerine) x (10 mol H2O/1 mol nitroglycerine)
Moles of N2 = (Number of moles of nitroglycerine) x (6 mol N2/1 mol nitroglycerine)
Moles of O2 = (Number of moles of nitroglycerine) x (1 mol O2/1 mol nitroglycerine)
Once you have the moles of each gas, you can calculate the total number of moles by summing them up:
Total moles = Moles of CO2 + Moles of H2O + Moles of N2 + Moles of O2
With the total number of moles, you can then use the ideal gas law equation, PV = nRT, to find the total pressure in the flask after the reaction is complete. Since you have a fixed volume (500 mL flask) and temperature (25.0°C), you can rearrange the equation to solve for pressure:
P = (nRT) / V
Substitute the values for total moles, ideal gas constant (R), temperature in Kelvin (convert from Celsius), and volume (convert from mL to L) into the equation to find the total pressure.
Lastly, to find the mole fraction of carbon dioxide, divide the moles of CO2 by the total moles:
Mole fraction of CO2 = Moles of CO2 / Total moles
Once you have the total pressure and mole fraction of carbon dioxide, you can subtract the vapor pressure of water (23.8 mmHg) from the final pressure to obtain the pressure contributed by the gases.
Note: Ensure you convert all units consistently (such as grams to moles, mL to L, etc.) and use the appropriate gas constant (R = 0.0821 L·atm/(mol·K) or R = 62.36 L·mmHg/(mol·K)) depending on the units of pressure you are working with.