Equilibrium in a closed vessel and the rate of reaction
Answers are for parents and teachers.
1
A reactant falls from 0.75 mol/L to 0.45 mol/L in 40 s. Find the average rate.
(0.75 − 0.45) ÷ 40 = 0.30 ÷ 40 = 0.0075 mol/(L·s).
2
Change a rate of 0.36 mol/(L·min) to mol/(L·s).
0.36 ÷ 60 = 0.0060 mol/(L·s).
3
Is Zn + H₂SO₄ → ZnSO₄ + H₂ in an open flask a complete or a reversible reaction, and why?
Complete, because the hydrogen gas escapes from the open flask, so the reverse cannot happen.
4
A student says: “At equilibrium nothing happens.” Write a two-sentence reply that uses the word rate.
Both the forward and the backward reactions go on. They go at equal rates, so the concentrations stay constant.
5
One concentration–time graph for a reactant falls steadily to zero. Another falls and levels off at 0.20 mol/L. Which one shows a reversible reaction at equilibrium? Explain.
The second one: the reactant is not used up, because the backward reaction makes it again, and the flat part means the concentration is constant.