Although the entire process that occurs when nitroglycerin explodes is very comp

Question

Although the entire process that occurs when nitroglycerin explodes is very complicated, we'll assume that it ail occurs according to the single chemical equation: Why are no values given for the enthalpy of formation for N_2(g) and 0_2(g)? Given the enthalpy of formation information above, calculate the heat generated in kj when 50.0 g of nitroglycerin explodes at 298 K and 1 atm. Assume that the heat generated then heats the gases produced in the reaction. What is the final temperature of the gas mixture? State ail assumptions Calculate the entropy change when this 50.0 g of nitroglycerin explodes. Assume that the entropy of the liquid nitroglycerin is negligible and explain why that's a reasonable assumption. Provide citations for any other data you need. Explain why this reaction is spontaneous at ail temperatures. Also explain whether the change in enthalpy or entropy is the greater driving force for the reaction being spontaneous. The standard enthalpy of atom combination, A infinity H degree , is defined to be the change in enthalpy when one mole of a compound forms from its constituent atoms in the gas phase at 298K and 1 bar pressure. For example, for N_2(g), atom combination refers to the process 2N(g) N_2(g) Given ail the information in the table above, write the balanced equation for the atom combination reaction that forms nitroglycerin and calculate the enthalpy of atom combination of nitroglycerin in units of kj/mol. (Can Hess's Law help you?) You should get a pretty large negative number. Why?

Explanation / Answer

dH0 = (-241.82x10 -393.51x12) - ( - 372.4 x 4) = - 5 650.7 kJ

For 1 mol nitroglycerin

dHo = - 5 650.7 kJ / 4 mol = - 1412.7 kJ/mol

50 g/227.1 g/mol = 0.220 mol

Heat released is

Q = 1412.7 kJ/mol x 0.220 = 439 kJ

c. The gases produced from 50 g nitroglycerin are

0.220 x10/4 = 0.550 mol H2O

0.220 x12/4 = 0.660 mol CO2

0.220 x6/4 = 0.330 mol N2

0.220 x1/4 = 0.055 mol O2

The molar specific heats at constant volume are:

H2O(g)     28.0 J/mol.K

CO2   28.2 J/mol.K

N2    20.6 J/mol.K

O2      21.1 J/mol.K      

The molar specific heats at constant pressure (assume complete expansion after explosion) are:

H2O(g)     37.5 J/mol.K

CO2 37.2 J/mol.K

N2    29.1 J/mol.K

O2      29.4 J/mol.K      

If you ignore the heat needed for the liquid water vaporization, then

Q = (0.550x37.5 + 0.660x37.2 + 0.330x29.1 + 0.055x29.4) x dT

439 000 J = (20.6 + 24.5 + 9.6 + 1.6) xdT

dT = 7800 K

d. General equation

dS0 = Sum nS0(products) – Sum mS0(reactants)

Use reference table for So values.

e. Look at the values and sign of dHo and TdSo

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