Textbook Question
For the reaction 2 Hg(l) + O2(g) → 2 HgO(s), ∆H = –43 kcal/mol (–180 kJ/mol).
a. Does entropy increase or decrease in this process? Explain.
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Ch.7 Chemical Reactions: Energy, Rate and Equilibrium
McMurry8th EditionFundamentals of GOBISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
Chapter 7, Problem 42
Which reaction is faster, one with Eact = +10 kcal/mol(+41.8 kJ/mol) or one with Eact = +5 kcal/mol(+20.9 kJ/mol)? Explain.
Verified step by step guidance1
Step 1: Understand the concept of activation energy (E_act). Activation energy is the minimum energy required for a chemical reaction to occur. A lower activation energy means that the reaction is more likely to occur at a given temperature, making it faster.
Step 2: Compare the given activation energies. The problem provides two activation energies: E_act = +10 kcal/mol (+41.8 kJ/mol) and E_act = +5 kcal/mol (+20.9 kJ/mol). Note that the second value is lower than the first.
Step 3: Recall the relationship between activation energy and reaction rate. According to the Arrhenius equation, the rate constant (k) of a reaction is inversely related to the activation energy. A lower activation energy results in a higher rate constant, meaning the reaction proceeds faster.
Step 4: Conclude which reaction is faster. Since the reaction with E_act = +5 kcal/mol (+20.9 kJ/mol) has a lower activation energy compared to E_act = +10 kcal/mol (+41.8 kJ/mol), it will be faster.
Step 5: Explain the reasoning. The reaction with the lower activation energy requires less energy for the reactants to reach the transition state, leading to a higher probability of successful collisions and a faster reaction rate.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Activation Energy (E_act)
Activation energy (E_act) is the minimum energy required for a chemical reaction to occur. It represents the energy barrier that reactants must overcome to transform into products. A lower activation energy indicates that a reaction can proceed more easily and quickly, as fewer energy inputs are needed to initiate the reaction.
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Reaction Rate
The reaction rate refers to the speed at which reactants are converted into products in a chemical reaction. It is influenced by several factors, including temperature, concentration, and the presence of catalysts. Generally, reactions with lower activation energies have higher rates because they require less energy to reach the transition state.
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Arrhenius Equation
The Arrhenius equation describes the relationship between the rate constant of a reaction and its activation energy, temperature, and a pre-exponential factor. It is mathematically expressed as k = A * e^(-E_act/RT), where k is the rate constant, A is the frequency factor, R is the gas constant, and T is the temperature in Kelvin. This equation illustrates that as activation energy decreases, the rate constant increases, leading to faster reactions.
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Related Practice
Textbook Question
For the reaction 2 Hg(l) + O2(g) → 2 HgO(s), ∆H = –43 kcal/mol (–180 kJ/mol).
b. Under what conditions would you expect this process to be spontaneous?
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Textbook Question
The following reaction is used in the industrial synthesis of polyvinyl chloride (PVC) polymer:
Cl2(g) + H2C=CH2(g) → ClCH2CH2Cl(l) ∆H = –52 kcal/mol (–218 kJ/mol)
a. Is ∆S positive or negative for this process?
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Textbook Question
Why does increasing concentration generally increase the rate of a reaction?
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Textbook Question
What is a catalyst, and what effect does it have on the activation energy of a reaction?
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Textbook Question
If a catalyst changes the activation energy of a forward reaction from 28.0 kcal/mol to 23.0 kcal/mol, what effect does it have on the reverse reaction?
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