Answer:
To find the amount of heat evolved when a certain amount of ammonia is produced, you need to use the concept of **stoichiometry** and the given value of **enthalpy change** for the reaction. Stoichiometry is the calculation of the quantities of reactants and products in a chemical reaction. Enthalpy change is the amount of heat absorbed or released by a system during a chemical reaction.
The given reaction is:
N 2 (g) + 3H 2 (g) → 2NH 3 (g); ΔH = –91.8 kJ
This means that for every 2 moles of ammonia produced, 91.8 kJ of heat is released. To find the amount of heat evolved when 8.66×10 5 g of ammonia is produced, you need to convert the mass of ammonia to moles, and then use the mole ratio and the enthalpy change to calculate the heat. The steps are as follows:
- Convert the mass of ammonia to moles using its molar mass. The molar mass of ammonia is 17.03 g/mol, so:
moles of ammonia = mass of ammonia / molar mass of ammonia
moles of ammonia = 8.66×10 5 g / 17.03 g/mol
moles of ammonia = 5.09×10 4 mol
- Use the mole ratio of ammonia to nitrogen in the balanced equation to find the moles of nitrogen that reacted. The mole ratio is 2:1, so:
moles of nitrogen = moles of ammonia / 2
moles of nitrogen = 5.09×10 4 mol / 2
moles of nitrogen = 2.55×10 4 mol
- Use the enthalpy change per mole of nitrogen to find the heat evolved. The enthalpy change is -91.8 kJ per mole of nitrogen, so:
heat evolved = moles of nitrogen x enthalpy change per mole of nitrogen
heat evolved = 2.55×10 4 mol x -91.8 kJ/mol
heat evolved = -2.34×10 6 kJ
Therefore, the amount of heat evolved when 8.66×10 5 g of ammonia is produced is -2.34×10 6 kJ. This means that the reaction is **exothermic**, which means that it releases heat to the surroundings.