Please explain these 2 questions. I truly don\'t get it. 5. What are the units o

Question

Please explain these 2 questions. I truly don't get it.

5. What are the units of k for the rate law: Rate k[A][B], when the concentration unit is mol/L? (a) s-1 (b) s (c) L mol-1 s1 (d) L2 mol-2 s (e) L2 s2 mol-2 6. Given: A 3B-2CD This reaction is first order with respect to reactant A and second order with respect to reactant B. If the concentration of A is doubled and the concentration of B is halved, the rate of the reaction would by a factor of- (a) increase, 2 (b) decrease, 2 (c) increase, 4 (d) decrease, 4 (e) not change

Explanation / Answer

5. Correct answer is third. Its a third order reaction. (Add power of A and B, 1+2=3)

General formula to calculate unit of k is (Mol/L)1-ns-1 , where n is the order of the reaction.

Putting n=3

(Mol/L)1-3s-1 gives (Mol/L)-2s-1 or L2mol-2s-1

6. Correct answer is second, decrease by a facor of two.

R = k [A] [B] 2 ...........................................(1)

Now, Concentration of [A] is doubles and [B] is halfed.

R' = k [2A] [1/2B]2

R' = k 2*[A] 1/4*[B]2

R' = k 2*1/4 [A] [B]2

R' = 1/2 R (From 1)

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