Question

An industrial chemist is studying the rate of the haber synthesis: n2 + 3h2 → 2nh3. starting with a closed reactor containing 1.35 mol/l of n2 and 0.35 mol/l of h2, she finds that the h2 concentration has fallen to 0.12 mol/l after 50. seconds. what is the average rate of reaction of h2 over this time? (enter in mol/liter/sec). what is the average rate of nh3 production for this example? (enter in mol/liter/sec)

Answer 1

1) Balanced chemical reaction: 3H₂ + N₂ → 2NH₃.

c₁(H₂) = 0.35 mol/L; initial concentration of hydrogen gas.

c₂(H₂) = 0.12 mol/L; concentration of hydrogen after 50 seconds.

Δt = 50 s.

the average rate of reaction = 1/3 · (Δc(H₂)/Δt).

the average rate of reaction of hydrogen = 1/3 · ((c₂(H₂)-c₁(H₂))/Δt).

the average rate of reaction = 1/3 · (0.12 mol/L - 0.35 mol/L) / 50 s.

the average rate of reaction of hydrogen = -0.00153 mol/Ls, it is negative because it measures the rate of disappearance of the reactants.

2) From chemical reaction: n(H₂) : n(NH₃) = 3 : 2.

c(NH₃) = 2 · 0.23 mol/L / 3.

c(NH₃) = 0.153 mol/L.

the average rate of reaction of ammonia = 1/2 · (0.153 / 50 s).

the average rate of reaction of ammonia = 0.00153 mol/L·s.

Answer 2

average rate of reaction of H2 over this time is calculated as

initial concentration of H2 minus final concentration of H2

That is
{(0.35mol/l -0.12mol/l) / 50 sec}= 4.6 x 10 ^-3 mol/l/sec