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Chapter 14: Problem 27

Define activation energy. What role does activation energy play in chemical kinetics?

Short Answer

Expert verified
Activation energy is the minimum energy required for a reaction to happen. It plays a vital role in chemical kinetics by influencing the rate of reactions. Higher activation energy results in slower reaction rates, and vice versa. Temperature also plays a role by affecting how many molecules can overcome the activation energy barrier.

Step by step solution

01

Define Activation Energy

Activation energy, often represented as \(E_a\), is the minimum amount of energy that reactants must possess for a chemical reaction to occur. It serves as a barrier to the progress of a reaction. No reaction can occur unless the reactant molecules possess this required amount of energy.
02

Explain Activation Energy’s Role in Chemical Kinetics

Activation energy plays a key role in chemical kinetics, which deal with the rate of reactions. Higher activation energy implies that fewer molecules will have sufficient energy to react, thus the reaction rate will be slower. Conversely, a lower activation energy means that more molecules can undergo the reaction, leading to a faster reaction rate. Temperature also affects this process. As temperature increases, more molecules possess the necessary energy to exceed the activation energy barrier, hence the reaction rate increases.

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Most popular questions from this chapter

What do we mean by the mechanism of a reaction?

Suggest experimental means by which the rates of the following reactions could be followed: (a) \(\mathrm{CaCO}_{3}(s) \longrightarrow \mathrm{CaO}(s)+\mathrm{CO}_{2}(g)\) (b) \(\mathrm{Cl}_{2}(g)+2 \mathrm{Br}^{-}(a q) \longrightarrow \mathrm{Br}_{2}(a q)+2 \mathrm{Cl}^{-}(a q)\) (c) \(\mathrm{C}_{2} \mathrm{H}_{6}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{H}_{2}(g)\)

The rate law for the reaction $$ 2 \mathrm{NO}(g)+\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{NOCl}(g) $$ is given by rate \(=k[\mathrm{NO}]\left[\mathrm{Cl}_{2}\right]\). (a) What is the order of the reaction? (b) A mechanism involving these steps has been proposed for the reaction $$ \begin{aligned} \mathrm{NO}(g)+\mathrm{Cl}_{2}(g) & \longrightarrow \mathrm{NOCl}_{2}(g) \\ \mathrm{NOCl}_{2}(g)+\mathrm{NO}(g) \longrightarrow & 2 \mathrm{NOCl}(g) \end{aligned} $$ If this mechanism is correct, what does it imply about the relative rates of these two steps?

Write the reaction rate expressions for these reactions in terms of the disappearance of the reactants and the appearance of products: (a) \(\mathrm{H}_{2}(g)+\mathrm{I}_{2}(g) \longrightarrow 2 \mathrm{HI}(g)\) (b) \(2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(g)\) (c) \(5 \mathrm{Br}^{-}(a q)+\mathrm{BrO}_{3}^{-}(a q)+6 \mathrm{H}^{+}(a q) \longrightarrow\) $$ 3 \mathrm{Br}_{2}(a q)+3 \mathrm{H}_{2} \mathrm{O}(l) $$

The reaction of \(\mathrm{G}_{2}\) with \(\mathrm{E}_{2}\) to form \(2 \mathrm{EG}\) is exothermic, and the reaction of \(\mathrm{G}_{2}\) with \(\mathrm{X}_{2}\) to form \(2 \mathrm{XG}\) is endothermic. The activation energy of the exothermic reaction is greater than that of the endothermic reaction. Sketch the potential energy profile diagrams for these two reactions on the same graph.
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