Question

When ammonia (NH3 ) reacts with dinitrogen oxide (N2O), the products of the reaction are H2O(l) and nitrogen gas.

a. Write a balanced chemical equation for this reaction.
b. How much heat is liberated (or consumed) when 345 mL of N (
g. (at 298.15 K and 100 000 Pa) are produced by this reaction.?

Answer 1

1) Balanced chemical reaction: 2NH₃ + 3N₂O → 3H₂O + 4N₂.
According to principle of mass conservation, number of atoms must be equal on both side of chemical reaction. There are eight nitrogen atoms, six hydrogen atoms and three oxygen atoms on both side of reaction, so chemical reaction is balanced.

2) ΔrH = ∑ΔfH(products) - ∑ΔfH(reactants).
ΔrH = 3·ΔfH(H₂O) + 4·ΔfH(N₂) - (2·ΔfH(NH₃) + 3·ΔfH(N₂O).
ΔrH = 3 mol ·(-285,5 kJ/mol) + 4 mol·(0 kJ/mol) - (2mol·(-46,1 kJ/mol) + 3mol·(82,05 kJ/mol)).
ΔrH = -1011,4 kJ.
Ideal gas law: p·V = n·R·T.
p = 100000 Pa = 0,987 atm.
T = 298,15 K.
V = 345 mL = 0,345 L.
R = 0,08206 L·atm/mol·K.
n(N₂) = 0,987 atm · 0,345 L ÷ 0,08206 L·atm/mol·K · 298,15 K.
n(N₂) = 0,014 mol.
4 mol : -1011,4 kJ = 0,014 mol : ΔH.
ΔH = -3,51 kJ.