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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Ch.7 Chemical Reactions: Energy, Rate and Equilibrium
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 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
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
Chapter 7, Problem 48a
The reaction between hydrogen gas and carbon to produce the gas known as ethylene is:
2 H2(g) + 2 C(s) → H2C=CH2(g), ∆G = +16.3 kcal/mol (+68 kJ/mol) 25 °C.
a. Is this reaction spontaneous at 25 °C?
Verified step by step guidance1
Step 1: Recall the concept of spontaneity in chemical reactions. A reaction is spontaneous if the Gibbs free energy change (∆G) is negative. If ∆G is positive, the reaction is non-spontaneous under the given conditions.
Step 2: Analyze the given information. The problem states that the Gibbs free energy change (∆G) for the reaction is +16.3 kcal/mol (+68 kJ/mol) at 25 °C. Since ∆G is positive, this suggests the reaction is not spontaneous under these conditions.
Step 3: Understand the implications of a positive ∆G. A positive ∆G means that the reaction requires an input of energy to proceed and will not occur on its own at the given temperature (25 °C).
Step 4: Consider the temperature dependence of ∆G. The spontaneity of a reaction can change with temperature, as ∆G is related to enthalpy (∆H), entropy (∆S), and temperature (T) by the equation: . However, no additional information about ∆H or ∆S is provided in this problem.
Step 5: Conclude that the reaction is non-spontaneous at 25 °C based on the positive ∆G value provided. If conditions such as temperature or energy input change, the spontaneity of the reaction may need to be re-evaluated.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Gibbs Free Energy (∆G)
Gibbs Free Energy (∆G) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. A negative ∆G indicates that a reaction is spontaneous, while a positive ∆G suggests that the reaction is non-spontaneous. In this case, the given ∆G of +16.3 kcal/mol indicates that the reaction is not spontaneous at 25 °C.
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Spontaneity of Reactions
The spontaneity of a chemical reaction refers to whether it can occur without external intervention. This is determined by the change in Gibbs Free Energy (∆G). If ∆G is negative, the reaction is spontaneous; if positive, it is non-spontaneous. Understanding this concept is crucial for predicting the behavior of chemical reactions under specific conditions.
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Temperature and Reaction Dynamics
Temperature plays a significant role in chemical reactions, influencing both the rate and spontaneity. The Gibbs Free Energy equation incorporates temperature, as it affects the enthalpy and entropy of the system. In this case, the reaction's non-spontaneity at 25 °C suggests that increasing the temperature may alter the reaction dynamics, potentially making it more favorable under different conditions.
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Related Practice
Textbook Question
What is meant by the term 'chemical equilibrium'? Must amounts of reactants and products be equal at equilibrium?
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Textbook Question
For the reaction C(s, diamond) → C(s, graphite), ∆G = -0.693 kcal/mol (-2.90 kJ/mol) at 25 °C.
a. According to this information, do diamonds spontaneously turn into graphite?
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Textbook Question
Write the equilibrium constant expressions for the following reactions:
a. 2 CO(g) + O2(g) ⇌ 2 CO2(g)
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Textbook Question
Why do catalysts not alter the amounts of reactants and products present at equilibrium?
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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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