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3.
(a) In chemical reaction kinetics, state what is meant by
(i) rate of reaction
(ii) reaction order
(iii) rate constant
Illustrate your answer by referring to the general gas phase reaction $\mathrm{A}+\mathrm{B} \rightarrow \mathrm{C}$
(b) Briefly, giving the relevant mathematical detail, describe two experimental methods for determining rate laws
(c) Cyclopropane isomerizes into propene when heated to $500^{\circ} \mathrm{C}$ in the gas phase. The extent of conversion for various initial pressures $\left(P_{0}\right)$ has been followed by allowing the reaction to proceed for a given time $(t)$ and then recording the final partial pressure $(P)$ of cyclopropane. The experimental data collected are:
\begin{tabular}{lcccccc}
$P_{0}(\mathrm{~Pa})$ & 20000 & 20000 & 30000 & 30000 & 50000 & 50000 \\
$t(\mathrm{~s})$ & 100 & 200 & 100 & 200 & 100 & 200 \\
$P(\mathrm{~Pa})$ & 18650 & 17300 & 27800 & 26000 & 46550 & 43300
\end{tabular}
(i) Using the data above, calculate the fractional conversion in each case and hence find the order of reaction with respect to cyclopropane.
(ii) What is the rate constant for the reaction under these conditions?
(iii) If you had data at a different temperature, how would you find the parameters in the Arrhenius expression for the rate constant?
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Answer from Sia

Posted 6 months ago

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a Answer

(i) Rate of reaction: speed at which reactants turn into products. (ii) Reaction order: exponent of reactant concentration in rate law. (iii) Rate constant: proportionality constant in rate law.

b Answer

Initial rates method and integrated rate laws method are two experimental methods for determining rate laws.

c Answer

(i) Fractional conversions calculated. (ii) Rate constant determined using integrated rate law. (iii) Arrhenius parameters found using ln($k$) vs. $1/T$ plot.

Key Concept

The rate of reaction, reaction order, and rate constant are fundamental concepts in chemical kinetics that describe how fast a reaction occurs and how reactant concentrations affect the rate.

Explanation

The rate of reaction indicates the speed of a chemical reaction. The reaction order shows the dependence of the rate on reactant concentrations, and the rate constant is a unique value for each reaction at a given temperature, relating the rate to the concentrations. Experimental methods like initial rates and integrated rate laws help determine these values, and the Arrhenius equation relates the rate constant to temperature.

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