Question

33. Consider the reaction: H2(g) + Br2(g) → 2 HBr (9) The graph shows the concentration of Br, as a function of time. 0.85 M Concentration (M) 068 ML 15s... Br To 0 50 100 150 a. Use the graph to calculate each quantity: i. the average rate of the reaction between 0 and 25 s ii. the instantaneous rate of the reaction at 25 s iii. the instantaneous rate of formation of HBr at 25

Answer 1

The Reaction carried out is :-

H2(g) + Br2(g) ===> 2HBr(g)

And the graph represents the conccentraction of Br2 (in M) with respect to time (in seconds)

when bromine reacts with hydrogen gas leads to formation of Hydrogen Bromide , therfore the concentration of bromine declines/decompose/Declearates to form desire product HBr.

Using graph we can caluate the given questions easily

i.) The average rate of the reaction betweem 0 and 25 seconds

Concentration of Br2 at 15 seconds is = 0.85M

and at 35 seconds is = 0.68 M (as per the graphical data)

therefore, to get the mid value

we need to take difference of (15 sec - 35 sec ) divide by 2

that is ( 0.85 - 0.68 )M / 2 = 0.17 M / 2 = 0.085M (We got the mid value of line between 15 sec and 35 sec )

so, the actual value of concentration of Br2 at 25 seconds is obtained by either adding 0.085M with 0.68M (Rate at 35 sec ) or subtrating with 0.85 M (rate at 15 sec)

Concentration of Br2 at 25 seconds is [0.68+0.085]=0.765M or [0.85-0.085]=0.765 M

[Br2]25 sec = 0.765M

[Br2]15 sec = 0.85M

Therefore , avaerage rate of reaction between 0 and 25 seconds is

Change in Concentration / time = [Br2]25 sec - [Br2]15 sec / 25 sec

= 0.765 M - 0.85 M / 25

= - 0.085 M /25

   average rate of reaction = - 0.0034 M/sec

ii.) The Instantaneous rate of the reaction at 25 seconds.

the instantaneous rate of reaction is the slope of line at 25 seconds

slope = Y2 -Y1 / t2 - t1 = 0.68 - 0.85 M / 35 - 15

= - 0.17/20

= -0.0085 M/sec.

iii.) The Instantaneous rate of formation of HBr at 25 seconds.

As the concentration of Br2 decrases /decomposes, the product HBr formation increases

order of the reaction is 2

rate of formation of desired product at 25 sec = avaerage rate of reaction * rate of reaction at 25 sec

So, the rate at which HBr is formed at 25 sec = - 0.0034M/sec * (- 0.0085M/sec)

= 2.89 x 10-5 M/sec