Question

Part A The rate constant for a certain reaction is k = 2.40×10−3 s−1 . If the initial reactant concentration was 0.650 M, what will the concentration be after 18.0 minutes? Express your answer with the appropriate units.

Part B

A zero-order reaction has a constant rate of 4.50×10⁻⁴M/s. If after 40.0 seconds the concentration has dropped to 4.50×10⁻²M, what was the initial concentration?

Express your answer with the appropriate units.

Answer 1

Based on the rate constant, the reaction is first order.

For first order reaction

lnC= lnCO-Kt

where C= Concentration at time t, CO= initial concentration= 0.650 K= Rate constant =2.4*10-3/sec, t=18 minutes=18*60=1080 minutes

lnC= ln(0.650)- 2.4*10^-3*1800 =ln(0.650)-4.32 =-4.751

C =exp(-4.751)= 0.008645M

Part B

For zero order reaction, C= CO-Kt

C =Concentration at time t = 4.5*10^-2M , K= rate constant= 4.5*10^-4 M/S, t=40 seconds

4.5*10^-2 =Co-4.5*10^-4*40, = Co-0.018

Co=0.063M