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Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
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Tutti i libri di testoMullins 1st EditionCh. 3 - Alkanes and Cycloalkanes: Properties and Conformational AnalysisProblema 64
Capitolo 2, Problema 64

Looking ahead In Chapter 5, we explain that the equilibrium constant (Keq) for a reaction can be calculated based on the difference in energy between reactants and products, according to the following equation:
Keq=e−ΔERTK_{eq}=e^{-\(\frac{\Delta E}{RT}\)}
Using this equation, calculate the equilibrium constant for the 'reaction' shown. [For the rest of the book, if not otherwise specified, assume room temperature (298K).]
Structural representation of a chemical equilibrium with two cyclic compounds, showing hydrogen and methyl groups.

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Step 1: Understand the equation provided. The equilibrium constant (Kₑ_q) is calculated using the formula: Kₑ_q = e ^ (-∆E / RT), where ∆E is the energy difference between reactants and products, R is the gas constant, and T is the temperature in Kelvin.
Step 2: Identify the values needed for the calculation. ∆E (energy difference) should be provided or calculated based on the reaction. R, the gas constant, is typically 8.314 J/(mol·K), and T is given as room temperature, 298 K.
Step 3: Substitute the values into the equation. Replace ∆E with the energy difference, R with 8.314 J/(mol·K), and T with 298 K in the formula: Kₑ_q = e ^ (-∆E / (8.314 × 298)).
Step 4: Simplify the exponent. Calculate the value of -∆E / (8.314 × 298) to determine the exponent for the base e.
Step 5: Compute the final value of Kₑ_q by evaluating the exponential function e ^ (-∆E / RT). This will give the equilibrium constant for the reaction.

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Equilibrium Constant (K_eq)

The equilibrium constant (K_eq) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given reaction. It provides insight into the extent to which a reaction proceeds, with values greater than 1 indicating a tendency towards products, and values less than 1 indicating a preference for reactants.
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02:19
The relationship between equilibrium constant and pKa.

Gibbs Free Energy (∆E)

Gibbs free energy (∆E) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. In the context of chemical reactions, a negative change in Gibbs free energy indicates that the reaction is spontaneous, while a positive change suggests non-spontaneity.
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05:02
Breaking down the different terms of the Gibbs Free Energy equation.

Temperature (T) and the Gas Constant (R)

Temperature (T) in the equation is typically expressed in Kelvin, and it influences the kinetic energy of molecules, affecting reaction rates and equilibria. The gas constant (R) is a proportionality constant that relates energy scales in thermodynamics, with a value of 8.314 J/(mol·K). Together, T and R are crucial for calculating K_eq using the relationship with Gibbs free energy.
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01:46
Why we use pKa instead of pH.
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