For the gas-phase chemical reaction: N2(g) + 3 H2(g) -> 2 NH3(g), how is the rate of formation of ammonia (d[NH3]/dt) stoichiometrically related to the rate of disappearance of hydrogen (-d[H2]/dt)?
Answer and explanation
Correct answer: C. d[NH3]/dt = -(2/3) * d[H2]/dt
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- Step 1: The general rate of reaction is expressed by dividing the rate of change of concentration of each species by its stoichiometric coefficient, with a negative sign for reactants:
- Step 2: Equating the terms for ammonia and hydrogen: .
- Step 3: Multiplying both sides by 2 gives: .
Answer
d[NH3]/dt = -(2/3) * (d[H2]/dt)
Why not the others: '-(3/2)' inverts the stoichiometric ratio (); '-2' ignores the stoichiometric coefficient of hydrogen (3); '-3' multiplies by 3 instead of dividing.
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