Textbook Question
Indicate whether each statement is true or false. (b) Exothermic reactions are faster than endothermic reactions.
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Ch.14 - Chemical Kinetics
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement111
- Ch.2 - Atoms, Molecules, and Ions166
- Ch.3 - Chemical Reactions and Reaction Stoichiometry138
- Ch.4 - Reactions in Aqueous Solution127
- Ch.5 - Thermochemistry104
- Ch.6 - Electronic Structure of Atoms109
- Ch.7 - Periodic Properties of the Elements107
- Ch.8 - Basic Concepts of Chemical Bonding102
- Ch.9 - Molecular Geometry and Bonding Theories120
- Ch.10 - Gases122
- Ch.11 - Liquids and Intermolecular Forces79
- Ch.12 - Solids and Modern Materials102
- Ch.13 - Properties of Solutions99
- Ch.14 - Chemical Kinetics153
- Ch.15 - Chemical Equilibrium83
- Ch.16 - Acid-Base Equilibria109
- Ch.17 - Additional Aspects of Aqueous Equilibria117
- Ch.18 - Chemistry of the Environment60
- Ch.19 - Chemical Thermodynamics109
- Ch.20 - Electrochemistry113
- Ch.21 - Nuclear Chemistry79
- Ch.22 - Chemistry of the Nonmetals52
- Ch.23 - Transition Metals and Coordination Chemistry57
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry7
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Not the one you use?Change textbook
Chapter 14, Problem 58a
Indicate whether each statement is true or false. (a) If you measure the rate constant for a reaction at different temperatures, you can calculate the overall enthalpy change for the reaction.
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Identify the relationship between the rate constant (k) and temperature, which is described by the Arrhenius equation: \( k = A e^{-\frac{E_a}{RT}} \), where \( A \) is the pre-exponential factor, \( E_a \) is the activation energy, \( R \) is the gas constant, and \( T \) is the temperature in Kelvin.
Understand that the enthalpy change (\( \Delta H \)) of a reaction is different from the activation energy (\( E_a \)). The activation energy is the energy barrier that must be overcome for reactants to transform into products, while the enthalpy change is the overall heat absorbed or released during the reaction.
Recognize that measuring the rate constant at different temperatures primarily provides information about the activation energy through the Arrhenius plot, where plotting \( ln(k) \) versus \( \frac{1}{T} \) gives a slope of \( -\frac{E_a}{R} \).
Conclude that while the activation energy can be derived from the temperature dependence of the rate constant, the overall enthalpy change of the reaction cannot be directly calculated from this data alone, as it requires additional thermodynamic information such as the heat capacities of reactants and products.
Determine the statement as false, since the rate constant measurements at different temperatures allow calculation of the activation energy, not the direct calculation of the overall enthalpy change of the reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Rate Constant and Temperature
The rate constant (k) of a chemical reaction is temperature-dependent, typically increasing with temperature due to higher kinetic energy of molecules. This relationship is described by the Arrhenius equation, which shows how k varies with temperature and activation energy. Understanding this concept is crucial for analyzing how temperature influences reaction rates.
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Rate Constant Units
Enthalpy Change (ΔH)
Enthalpy change (ΔH) is a measure of the heat absorbed or released during a chemical reaction at constant pressure. It reflects the difference in energy between reactants and products. While the rate constant can provide insights into reaction kinetics, ΔH is determined through thermodynamic principles, often requiring calorimetric data or Hess's law for accurate calculation.
Van 't Hoff Equation
The Van 't Hoff equation relates the change in the equilibrium constant of a reaction to the change in temperature and the enthalpy change of the reaction. It allows for the calculation of ΔH if the equilibrium constants at two different temperatures are known. This equation is essential for linking thermodynamics and kinetics, particularly in the context of temperature effects on reaction rates.
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Related Practice
Textbook Question
Based on their activation energies and energy changes and assuming that all collision factors are the same, rank the following reactions from slowest to fastest. (a) Ea = 45 kJ>mol; E = -25 kJ>mol (b) Ea = 35 kJ>mol; E = -10 kJ>mol (c) Ea = 55 kJ>mol; E = 10 kJ>mol
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Textbook Question
The gas-phase reaction Cl(g) + HBr(g) → HCl(g) + Br(g) has an overall energy change of -66 kJ. The activation energy for the reaction is 7 kJ. (b) What is the activation energy for the reverse reaction?
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Textbook Question
Indicate whether each statement is true or false. (c) Increasing the reaction temperature increases the fraction of successful collisions between reactants.
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