Heats of reaction equation

[markosheehan]

hello
I am stuck on this question
The decomposition of nitroglycerine is given by the following

2C3H5N3O9 = 6CO2 + 5H2O + 3N2 + 1/2O2

using the following heats of formation, determine the energy released in the decomposition of of nitroglycerine.

heats of formation of CO2(g), and H2O(l), C3H5N3O9 are -393, 242 and -364 kJ/mole, respectively

I am using hesses law to try and work this out
I multiply the heat of formation equation of Co2 by 6 and reverse it and multiply the heat of formation equation of H2O by 5.

I multiply the heat of formation equation of C3H5N3O9 by 2 and reverse it aswell.

when I do all of this a lot of the compounds cancel but I am left with 5/2 o2 on the left hand side of the final equation which can not be there

 

[jvicens]

Thank you for your post. I can help you with your question about the decomposition of nitroglycerine.

Firstly, you are correct in using Hess's law to determine the energy released in the decomposition of nitroglycerine. However, there seems to be a mistake in your calculations. Let me walk you through the steps:

1. Start by writing the given equation for the decomposition of nitroglycerine: 2C3H5N3O9 = 6CO2 + 5H2O + 3N2 + 1/2O2.

2. Next, write the equation for the formation of CO2: C + O2 = CO2. We need to multiply this equation by 6 and reverse it to match the number of CO2 molecules in the decomposition equation. This gives us: 6CO2 = 6C + 6O2.

3. Similarly, write the equation for the formation of H2O: H2 + 1/2O2 = H2O. Multiply this equation by 5 and reverse it to match the number of H2O molecules in the decomposition equation. This gives us: 5H2O = 5H2 + 5/2O2.

4. Finally, write the equation for the formation of C3H5N3O9: 3C + 5H2 + 3N2 + 9/2O2 = C3H5N3O9. Multiply this equation by 2 and reverse it to match the number of C3H5N3O9 molecules in the decomposition equation. This gives us: 2C3H5N3O9 = 6C + 10H2 + 6N2 + 9O2.

5. Now, add all the equations together to cancel out the common compounds on both sides. This gives us the final equation: 2C3H5N3O9 = 6CO2 + 5H2O + 3N2 + 1/2O2.

6. To calculate the energy released in the decomposition of nitroglycerine, we need to use the given heats of formation. Substitute the values in the final equation, and we get: ΔH = (6 x -393) + (5 x -242) + (3 x 0) +