Ch. 2 - Water and Carbon: The Chemical Basis of Life

Freeman - Biological Science 8th Edition

Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook

Freeman 8th Edition

Ch. 2 - Water and Carbon: The Chemical Basis of Life

Problem 4

Chapter 2, Problem 4

What factors determine whether a chemical reaction is spontaneous or not?

Verified step by step guidance

Understand that the spontaneity of a chemical reaction is determined by the Gibbs free energy change (ΔG). A reaction is spontaneous if ΔG < 0 (negative).

Recall the formula for Gibbs free energy:

ΔG = ΔH - TΔS

, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.

Analyze the role of enthalpy (ΔH): If ΔH is negative (exothermic reaction), it favors spontaneity. If ΔH is positive (endothermic reaction), it works against spontaneity.

Consider the role of entropy (ΔS): If ΔS is positive (increase in disorder), it favors spontaneity. If ΔS is negative (decrease in disorder), it works against spontaneity.

Evaluate the temperature (T): At higher temperatures, the TΔS term becomes more significant. This means that reactions with a positive ΔS are more likely to be spontaneous at higher temperatures, while reactions with a negative ΔS may require lower temperatures to be spontaneous.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict whether a chemical reaction will occur spontaneously at constant temperature and pressure. A reaction is spontaneous if the change in Gibbs Free Energy (ΔG) is negative, indicating that the products have lower energy than the reactants. This concept integrates both enthalpy and entropy, providing a comprehensive criterion for spontaneity.

Enthalpy and Entropy

Enthalpy (H) is a measure of the total heat content of a system, while entropy (S) quantifies the degree of disorder or randomness. The relationship between these two properties is crucial in determining spontaneity. A reaction can be spontaneous if it releases heat (exothermic, ΔH < 0) or increases disorder (ΔS > 0), or both, as reflected in the Gibbs Free Energy equation: ΔG = ΔH - TΔS.

Temperature's Role

Temperature (T) plays a significant role in determining the spontaneity of a reaction, particularly through its influence on entropy. As temperature increases, the impact of entropy on Gibbs Free Energy becomes more pronounced. For reactions where entropy increases (ΔS > 0), higher temperatures can favor spontaneity, even if the reaction is endothermic (ΔH > 0), making temperature a critical factor in the spontaneity of chemical reactions.

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Related Practice

Textbook Question

Which of the following occurs when a covalent bond forms?

a. Electrons in valence shells are transferred from one atom to another.

b. Electrons in valence shells are shared between atoms.

c. Partial charges on polar molecules interact.

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Textbook Question

What are the defining characteristics of a condensation reaction?

a. Two monomers are covalently bonded together and a water molecule is produced.

b. Two monomers are covalently bonded together and a water molecule is used up.

c. A polymer is broken down into monomers and a water molecule is produced.

d. A polymer is broken down into monomers and a water molecule is used up.

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Textbook Question

Which of these functional groups is known to be used for storing large amounts of chemical energy?

a. Amino group

b. Carbonyl group

c. Phosphate group

d. Sulfhydryl group

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Textbook Question

Which of these molecules would you predict to have the largest number of polar covalent bonds based on their molecular formulas?

a. C₂H₆O(ethanol)

b. C₂H₆(ethane)

c. C₂H₄O₂(acetic acid)

d. C₃H₈O (propanol)

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Textbook Question

Locate fluorine (F) on the partial periodic table provided in Figure 2.2. Predict its relative electronegativity compared to hydrogen, sodium, and oxygen. State the number and type of bond(s) you expect it would form if it reacted with sodium (Na).

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Textbook Question

If you were given a solution that has a pH of 8.5, what would be its concentration of protons? What is the difference in proton concentration between this solution and one that has a pH of 7?

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