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Chapter 8: Problem 17

For an endothermic reaction, where \(\Delta \mathrm{H}\) represents the enthalpy of the reaction in \(\mathrm{kJ} /\) mole. The minimum value for the energy of activation will be a. less than \(\Delta \mathrm{H}\) b. zero c. more than \(\Delta \mathrm{H}\) d. equal to \(\Delta \mathrm{H}\)

Short Answer

Expert verified
The minimum value for the energy of activation is more than \( \Delta \mathrm{H} \), so the answer is c.

Step by step solution

01

Understand the Reaction Type

In an endothermic reaction, energy is absorbed from the surroundings. The enthalpy change, \( \Delta \mathrm{H} \), is positive, indicating that the products have higher energy than the reactants.
02

Define Activation Energy

Activation energy is the minimum energy required for a chemical reaction to occur. It represents the energy barrier that must be overcome for the reactants to be transformed into products.
03

Relate Activation Energy and Enthalpy

In endothermic reactions, the activation energy must be enough to not only provide the energy for the reaction to proceed but also to produce the enthalpy change \( \Delta \mathrm{H} \). Therefore, activation energy is generally larger than \( \Delta \mathrm{H} \).
04

Conclusion

Since activation energy must overcome both the initial energy needed for the reaction and account for the energy absorbed (\( \Delta \mathrm{H} \)), it is greater than \( \Delta \mathrm{H} \). Thus, the minimum value for the energy of activation is more than \( \Delta \mathrm{H} \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Endothermic Reactions
Endothermic reactions are fascinating events in chemical processes where energy is absorbed rather than released. This means these reactions require energy from their surroundings to take place. A classic example can be found in the melting of ice. During endothermic reactions, the reactants absorb energy, causing their surroundings to cool down.
Characteristics of Endothermic Reactions:
  • They usually feel cold to the touch since energy is absorbed.
  • Have a positive enthalpy change, \( \Delta \mathrm{H} > 0 \).
  • Typically involve breaking stronger bonds and forming weaker ones.
Understanding the nature of these reactions helps in predicting how energy interactions will play out, which is crucial for fields ranging from chemistry to biology and environmental science.
Enthalpy Change
The concept of enthalpy change is central to understanding chemical reactions. Enthalpy, denoted as \( \Delta \mathrm{H} \), measures the total heat content of a system. For reactions, it tells us whether a reaction is endothermic (absorbs heat) or exothermic (releases heat).
Key Points about Enthalpy Change:
  • Endothermic reactions have a positive \( \Delta \mathrm{H} \) indicating that energy is absorbed.
  • It is calculated by subtracting the enthalpy of reactants from products: \( \Delta \mathrm{H} = \mathrm{H}_{\text{products}} - \mathrm{H}_{\text{reactants}} \).
  • Each reaction has a distinct enthalpy change value influenced by reactant and product characteristics.
Knowing the enthalpy change helps us understand how much energy a reaction will need or release, aiding in designing processes like those in industrial chemistry.
Energy Barrier
In chemical reactions, an energy barrier is the energetic hurdle that reactants must overcome to convert into products. This is often described in terms of activation energy, which represents this required energy input.
Features of the Energy Barrier:
  • It determines the speed and feasibility of a reaction.
  • Higher energy barriers mean slower reactions since fewer molecules have sufficient energy to react.
  • In endothermic reactions, the energy barrier includes both the activation energy and the enthalpy change needed.
Recognizing the energy barrier's role is essential in fields like chemical engineering, where enhancing reaction rates is often desired through catalysts that lower these barriers.
Chemical Reactions
Chemical reactions are processes in which substances, known as reactants, convert into different substances called products. This transformation involves breaking and forming bonds, during which energy is either absorbed or released.
Important Aspects of Chemical Reactions:
  • They involve the rearrangement of atoms to create new molecules.
  • Reactions can be categorized as exothermic or endothermic based on their energy exchange.
  • Chemical reactions follow the law of conservation of mass, meaning matter is neither created nor destroyed.
Understanding these concepts provides insight into many natural and industrial processes, allowing scientists and engineers to predict outcomes and manipulate reactions for various applications.

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Most popular questions from this chapter

Two reactions \(\mathrm{X} \rightarrow\) Products and \(\mathrm{Y} \rightarrow\) products have rate constant \(\mathrm{k}_{\mathrm{x}}\) and \(\mathrm{k}_{\mathrm{Y}}\) at temperature \(\mathrm{T}\) and activation energies \(\mathrm{E}_{\mathrm{x}}\) and \(\mathrm{E}_{\mathrm{Y}}\) respectively. If \(\mathrm{k}_{\mathrm{x}}>\) \(\mathrm{k}_{\mathrm{r}}\) and \(\mathrm{E}_{\mathrm{x}}<\mathrm{E}_{\mathrm{Y}}\) and assuming that for both the reaction is same, then a. At lower temperature \(\mathrm{k}_{\mathrm{Y}}>\mathrm{k}_{\mathrm{x}}\) b. At higher temperature \(\mathrm{k}_{\mathrm{x}}\) will be greater than \(\mathrm{k}_{\mathrm{y}}\) c. At lower temperature \(\mathrm{k}_{\mathrm{x}}\) and \(\mathrm{k}_{\mathrm{Y}}\) will be close to each other in magnitude d. At temperature rises, \(\mathrm{k}_{\mathrm{x}}\) and \(\mathrm{k}_{\mathrm{Y}}\) will be close to each other in magnitude

Which of the following statements are correct? (1) Order of a reaction can be known from experimental results and not from the stoichiometry of reaction. (2) Molecularity a reaction refers to (i) each of the elementary steps in (an overall mechanism of) a complex reaction or (ii) a single step reaction (3) Overall molecularity of a reaction may be determined in a manner similar to overall order of reaction (4) Overall order of a reaction \(\mathrm{A}^{\mathrm{m}}+\mathrm{B}^{\mathrm{n}} \rightarrow \mathrm{AB}_{\mathrm{x}}\) is \(\mathrm{m}+\mathrm{n} .\) Select the correct answer using the following codes: a. 2 and 3 b. 1,3 and 4 c. 2,3 and 4 d. 1,2 and 3

Consider the following statements: (1) Rate of a process is directly proportional to its free energy change. (2) The order of an elementary reaction step can be determined by examining the stoichiometry. (3) The first order reaction describe exponential time coarse. Of the statements a. 1 and 2 are correct b. 1 and 3 are correct c. 2 and 3 are correct d. 1,2 and 3 are correct

Which of the following is/are examples of unimolecular reactions? a. \(2 \mathrm{NO}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{NOCl}\) b. \(\mathrm{O}_{3} \rightarrow \mathrm{O}_{2}+\mathrm{O}\) c. C=CCCCC d. \(\mathrm{NO}+\mathrm{O}_{3} \rightarrow \mathrm{NO}_{2}+\mathrm{O}_{2}\)

In Arrhenius equation: \(\mathrm{k}=\mathrm{Ae}^{-\mathrm{Ea} \mathrm{RT}}\) a. The exponential factor has the units of reciprocal of temperature. b. The pre-exponential factor has the units of rate of the reaction. c. The pre-exponential factor has the units of rate constant of the reaction. d. The exponential factor is a dimensionless quantity.
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