Rate of Reaction

Question

2KCl(aq) + Pb(NO₃)₂(aq) → PbCl₂(s) + 2KNO₃(aq)

The concentration of Pb(NO₃)₂ is 0.849 M at the start of the reaction, and 0.535 M after 65 seconds. The initial concentrations of the products are zero.

1.What is the average rate of change (in M/min) of KNO₃ in the first 65 seconds.

2.What is the concentration (in M) of KNO₃ after 65 seconds.

Answer 1

Assuming first order:

(1). -∆ [Pb(NO₃)₂/∆t = 1/2∆ [KNO₃]/∆t

∆ [Pb(NO₃)₂ = 0.849 M - 0.535 M = 0.313 M

∆t = 65 sec x 1 min/60 sec = 1.083 min

0.313 M/1.083 min = 0.289 M/min = rate of disappearance of Pb(NO3)2

0.289 = 1/2 x

x = 0.578 M/min = rate of change of KNO3 in the first 65 seconds.

(2). Concentration of KNO3 after 65 sec:

0.578 M/min x 1.083 min = 0.626 M