15.23 part C

[diangelosoriano]

Determine the rate constant for each of the following first-order reactions:

Part C) 2A-->B+C,given that[A]0 =0.153molxL^-1 and that after 115 s the concentration of B rises to 0.034 molxL^-1.

I am confused as to where to start with this problem?

[Tiffany Dao 1A]

you can find [A] at 115 seconds by converting the [B].
[A] = 0.153 molA/L - [0.034 molB/L x (2 molA/1 molB)]
then you can use ln[A] = -kt + ln{A]o

[diangelosoriano]

you can find [A] at 115 seconds by converting the [B].
[A] = 0.153 molA/L - [0.034 molB/L x (2 molA/1 molB)]
then you can use ln[A] = -kt + ln{A]o

Why do we subtract [0.034 molB/L x (2 molA/1 molB)]? Is there an equation on the formula sheet that we derive this from?

[Xin He 2L]

We would subtract B from A because B is created from A, so when B increases, A decreases. After the subtraction, you'll find the new value for A which you then plug into the equation and solve for the time elapsed.