Chemistry Help Please!

Question

The rate of the reaction in terms of the "disappearance of reactant" includes the change in the concentration of the reactant, the time interval, and the coefficient of the reactant. Consider the following reaction:

2A+3B→3C+2D

The concentrations of reactant A at three different time intervals are given. Use the following data to determine the average rate of reaction in terms of the disappearance of reactant A between time=0s and time=20s.

Time (s )   0        20        40
[A](M) 0.0400 0.0240 0.0180

 

*What is the rate of reaction?*

Express your answer in molar concentration per second to three significant figures.

Answer 1

Hi Meg,

 

The average rate of reaction can be calculated from the change in [A] versus time.  For the time interval between 0 and 20 seconds:

 

Rate = (0.0240 M - 0.0400 M)/20 sec

 

Rate = -0.000800 M/sec (to three sig figs). 

 

Note that the rate is negative because A is being consumed.  Also, this is an AVERAGE rate for the time increment given.  The reaction appears to slow down quite a bit in the second 20 sec interval (concentration of A doesn't decrease as fast).

 

Hope this helps.