The decomposition of phosphorus pentachloride in the presence of moisture takes place by the following mechanism. The rate equation for this reaction will be:
Correct answer: B. Rate = k [PCl5][H2O]
- A. Rate = k [POCl3][H2O]3
- B. Rate = k [PCl5][H2O]
- C. Rate = k [PCl5][H2O]4
- D. Rate = [PCl5][H2O]
Explanation
For the rate equation, the reactants of ONLY the rate-determining step, which is the slow step, are taken into account in a multi-step reaction, NOT the overall equation or the fast step. Since the slow step here consists of one mole of PCL5 and one mole of H2O in the reactants, the rate equation will contain these two substances, each raised to the power 1, which is reflected in option B only. Option A takes into account the fast step only. Option C takes into account the overall reaction. Option D does not have the rate constant k mentioned in the question.
Last updated
About Reaction Kinetics
Reaction kinetics relates reaction rate to concentration, temperature, surface area and catalysts. Questions cover rate laws, reaction order, rate constants, activation energy and the activated complex, including how a catalyst lowers the activation energy without changing the overall energy change or equilibrium position.
Practise Reaction Kinetics
573 free Reaction Kinetics MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Exams that ask Chemistry questions like this
Chemistry is on 12 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
Related questions
100 g of a substance decays slower than 50 g of the same substance. The order of decay follows kinetics:
12.Rate of disappearance of reactant is equal to
13.Rate of reaction, when concentration of reactants are taken as unity is called
14.Order of reaction of N2O5→2N2O5+ O2
16.Which order of reaction obeys the relation t1/2= 1/Ka