Question

While the majority component of air is nitrogen (N2), the gas is very unreactive because of its stability due to the triple bonds that hold the nitrogen atoms together. Nitrogen gas is, therefore, relatively unavailable for chemical reactions. One of the few ways to “fix” nitrogen, making a nitrogen compound from the elemental nitrogen in the atmosphere, is the Haber process (aka Haber - Bosch process). In this reaction, nitrogen gas combines with hydrogen gas to yield ammonia. The enthalpy ( ΔH) of this reaction is - 92.22 kJ/mol. This process was discovered by the German chemist Fritz Haber in the early twentieth century. Through extensive experimentation, Haber found the conditions that would produce adequate yields (at a temperature of about 500 oC and a pressure of about 200 atm). This process holds a significant importance today because of its application in the industrial production of ammonia - based fertilizer. Idn

1918, Haber received the Nobel Prize in Chemistry for work. However, a lot of controversy followed the Nobel Prize award. For this experiment, 17.15grams of nitrogen gas and 10.95 grams of hydrogen gas are allowed to react in the reaction vessel. The ammonia vapor that is produced is then condensed, liquefied, and collected into a collection vessel.

1. Is the Haber process an exothermic or endothermic reaction?

2. Write a balanced thermochemical equation with phase labels for the Haber process with theheat energy as part of the equation.

3. What is the theoretical yield of ammonia (in grams) if 17.15 grams of nitrogen gas and 10.95 grams of hydrogen gas are allowed to react?

4. Based on your theoretical yield, what is the percent yield of ammonia if only 11.5 grams of ammonia is produced?

5. How much heat energy (in kJ) will be absorbed or released if 11.5 grams of ammonia is produced? State whether the energy will be absorbed or released.

Answer 1

A) Given = -92.22 KJ/mol for each 1 mole of NH₃ produced

i.e. the -ve sign indicates that the system is loosing energy.

Hence the Haber's process is an exothermic process.

B) Since ​ is given for 1 mole of ammonia, the balanced equation can be written as followed

C) Given mass of N2= 17.15 gms

No. of moles of N2 = mas/ M wt = 17.15/ 28 = 0.6125 moles

mass of H2 = 10.95 gms

No. of moles of H2 = 10.95 / 2 = 5.475 moles

From the above balanced equation 1 mole of N₂ reacts with 1.5 moles of H₂ to produce 1 mole of NH₃

i.e. 28 gms N₂ + 3 gms H₂​ 17 gms NH₃

From the give data it can be observed that N₂ is the limiting reagent and H₂ is excess reagent.

Hence 0.6125 moles of N₂ + 2x0.6125 moles of H₂​ 0.6125 moles of NH₃

Theoritical mass of NH₃ = no. of moles x M. wt = 0.6125 x 17 = 10.4125 gms

4) Given mass of NH₃ = 11.5 gms

from the above calculations theoritical mass of NH₃ = 10.4125 gms

Hence

% yield = (11.5/ 10.4125) x 100 = 110.44 %

5) From the given data for 1 mole NH₃ formed 92.22 KJ heat is released

Hence for 0.6125 moles of NH3 heat released = 0.625 x 92.22 = 56.48475 KJ

hence for the experiment 56.484 KJ heat is released; i.e H = -56.484 KJ.