Advertisements
Advertisements
Question
For the decomposition of azoisopropane to hexane and nitrogen at 543 K, the following data are obtained.
| t (sec) | P(mm of Hg) |
| 0 | 35.0 |
| 360 | 54.0 |
| 720 | 63.0 |
Calculate the rate constant.
Advertisements
Solution
Azoisopropane decomposes according to the following equation:
\[\ce{(CH3)2CHN = NCH(CH3)2_{(g)} -> N2_{(g)} + C6H14_{(g)}}\]
This action is a first-order reaction.
Initial pressure (P0) = 35.0 mm Hg
Decrease in pressure of azoisopropane after time t is P.
Increase in N2 pressure = `P_(N_2)`
Increase in the pressure of hexane = `P_(C_6H_14)`
Total pressure of the mixture (Pt) = `P_A + P_(N_2) + P_(C_6H_14)`
Pt = (P0 – P) + P + P
Pt = P0 + P
P = Pt – P0
PA = P0 – (Pt – P0) = 2P0 – Pt
But PA ∝ a − x and P0 ∝ Pt
k = `2.303/t log P_0/(2P_0 - P_t)`
When t = 360 s,
k = `2.303/360 log 35/(2 xx 35 - 54)`
= `2.303/360 log 35/16`
= `2.303/360 log 2.1875`
= `2.303/360 xx 0.339`
k = 2.17 × 10–3 s–1
When, t = 720 s,
k = `2.303/720 log 35/(2 xx 35 - 63)`
= `2.303/720 log 35/7`
= `2.303/720 (log 35 - log 7)`
= `2.303/720 (1.544 - 0.845)`
= `2.303/720 xx 0.699`
k = 2.23 × 10–3 s–1
Rate constant = `((2.17 + 2.23))/2 xx 10^-3 s^-1`
= 2.20 × 10–3 s–1
APPEARS IN
RELATED QUESTIONS
A first order reaction has a rate constant 1.15 × 10−3 s−1. How long will 5 g of this reactant take to reduce to 3 g?
Time required to decompose SO2Cl2 to half of its initial amount is 60 minutes. If the decomposition is a first order reaction, calculate the rate constant of the reaction.
In a pseudo first order hydrolysis of ester in water, the following results were obtained:
| t/s | 0 | 30 | 60 | 90 |
| [A]/mol L−1 | 0.55 | 0.31 | 0.17 | 0.085 |
Calculate the average rate of reaction between the time interval 30 to 60 seconds.
The rate constant for a first order reaction is 60 s−1. How much time will it take to reduce the initial concentration of the reactant to its `1/16`th value?
The time required for 10% completion of a first order reaction at 298 K is equal to that required for its 25% completion at 308 K. If the value of A is 4 × 1010 s−1. Calculate k at 318 K and Ea.
A first order reaction is 50% complete in 25 minutes. Calculate the time for 80% completion of the reaction.
Straight line graph for first order reaction is obtained between ____________.
State a condition under which a bimolecular reaction is kinetically first order reaction.
With the help of an example explain what is meant by pseudo first order reaction.
The rate constant of a first order reaction is 6.9 × 10–3s–1. How much time will it take to reduce the initial concentration to its 1/8th value?
In a first order reaction the concentration of reactants decreases from 400mol L-1 to 25 mol L-1 in 200 seconds. The rate constant for the reaction is ______.
Observe the graph shown in figure and answer the following questions:
- What is the order of the reaction?
- What is the slope of the curve?
- Write the relationship between k and t1/2 (half life period).
A definite volume of H2O2 undergoing spontaneous decomposition required 22.8 c.c. of standard permanganate solution for titration. After 10 and 20 minutes respectively the volumes of permanganate required were 13.8 and 8.25 c.c. The time required for the decomposition to be half completed is ______ min.
The slope in the plot of `log ["R"]_0/(["R"])` Vs. time for a first-order reaction is ______.
Slove: \[\ce{2NOBr -> 2NO_{2(g)} + Br_{2(g)}}\]
For the above reaction, the rate law is rate = k[NOBr]2. If the rate of reaction is 6.5 × 10−6 mol L−1 s−1 at 2 × 10−3 mol L−1 concentration of NOBr, calculate the rate constant k for the reaction.
The rate constant for the reaction:
\[\ce{2N2O_{(s)} ->2N2O4_{(g)}}\] is 4.98 × 10-4 s-1.
The order of the reaction is ______.
Show that `t_(1/2)= 0.693/k` for first reaction.
Write the unit of rate constant [k] for the first order reaction.
