Question

Rate law for hydrolysis of thioacetamide (CH3CSNH2), is rate = k[H+][CH3CSNH2]. CH3CSNH2(aq) + H2O(l) ->H2S(g) + CH3CONH2(aq). If, during course of reaction, some solid sodium hydroxide is added to reaction mixture, then A) reaction rate decreases, but k remains same B) the reaction rate remains the same, but k decreases C) reaction rate increases, but k remains same D) there is no change in reaction rate or rate constant E) reaction rate remains same, but k increases

Answer 1

Rate law for hydrolysis of thioacetamide (CH3CSNH2), is
rate = k[H+][CH3CSNH2].
CH3CSNH2(aq) + H2O(l) ->H2S(g) + CH3CONH2(aq).

If, during course of reaction, some solid sodium hydroxide is added to reaction mixture, then
A) reaction rate decreases, but k remains same
B) the reaction rate remains the same, but k decreases
C) reaction rate increases, but k remains same
D) there is no change in reaction rate or rate constant
E) reaction rate remains same, but k increases

Answer:
Adding NaOH will increase [OH-] and decrease [H+] as [H+] = kw/[OH-] = 1.0E-14/[OH-]

(A) is correct
rate = k*[H+]*[CH3CSNH2] decrease as H+ decrease due to addition of NaOH.
rate constant does not depend on H+, so k remains same.

(B) is wrong because H+ will decrease by adding H+.

C) is wrong as reaction rate decreases, as H+ decreases

D)is wrong as reaction rate decreases, as H+ decreases

E) is wrong as reaction rate decreases, as H+ decreases