Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook

Mullins 1st Edition

Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics

Problem 19

Chapter 4, Problem 19

If the following reaction is favorable, what can we say about the sign of ∆H°? Explain your answer.

Verified step by step guidance

Step 1: Understand the concept of enthalpy change (∆H°). ∆H° represents the change in enthalpy (heat content) during a chemical reaction under standard conditions. It indicates whether a reaction absorbs or releases heat.

Step 2: Recall the relationship between reaction favorability and ∆H°. A reaction is considered favorable if it proceeds spontaneously under given conditions. While spontaneity is primarily determined by Gibbs free energy (∆G°), ∆H° plays a role in determining ∆G° along with entropy (∆S°).

Step 3: Consider the sign of ∆H° for favorable reactions. If a reaction releases heat (exothermic), ∆H° is negative, which often contributes to making the reaction favorable. Conversely, if a reaction absorbs heat (endothermic), ∆H° is positive, but the reaction can still be favorable if entropy changes significantly.

Step 4: Analyze the context of the problem. Since the question asks about the sign of ∆H° for a favorable reaction, we can infer that a negative ∆H° (exothermic reaction) is more likely to contribute to favorability, as it lowers the energy of the system.

Step 5: Conclude that for a favorable reaction, the sign of ∆H° is typically negative, but it is important to consider other factors like entropy and temperature that influence the overall spontaneity (∆G°).

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

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

Enthalpy Change (∆H°)

Enthalpy change (∆H°) is a measure of the heat content of a system at constant pressure. A negative ∆H° indicates that a reaction releases heat (exothermic), while a positive ∆H° signifies that the reaction absorbs heat (endothermic). Understanding the sign of ∆H° is crucial for predicting the favorability of a reaction, as exothermic reactions are generally more favorable.

Gibbs Free Energy (∆G)

Gibbs Free Energy (∆G) combines enthalpy and entropy to determine the spontaneity of a reaction. A reaction is considered favorable (spontaneous) when ∆G is negative. The relationship between ∆G, ∆H, and entropy (T∆S) is given by the equation ∆G = ∆H - T∆S, where T is the temperature in Kelvin. This concept is essential for understanding how enthalpy influences reaction favorability.

Thermodynamic Favorability

Thermodynamic favorability refers to the likelihood of a reaction occurring under standard conditions. A reaction is thermodynamically favorable if it leads to a decrease in free energy (negative ∆G). This often correlates with a negative ∆H° for exothermic reactions, suggesting that heat is released, which can drive the reaction forward. Understanding this concept helps in predicting the behavior of chemical reactions.

Recommended video:

Guided course

08:51

Kinetic vs. Thermodynamic Control

Related Practice

Textbook Question

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.

(c)

views

Textbook Question

Draw a reaction coordinate diagram for a one step reaction that has the following values of E_a and ∆H. (a) E_a = 9 kcal/mol ; ∆H° = + 4 kcal/mol

views

Textbook Question

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.

(b) 2 C₆H₁₄(l) + 19 O₂(g) → 12 CO₂(g) + 14 H₂O(g)

views

Textbook Question

Draw a reaction coordinate diagram for a one step reaction that has the following values of E_a and ∆H. (b) E_a = 2 kcal/mol ; ∆H° = -17 kcal/mol

views

Textbook Question

For each of the following processes, indicate whether you expect ∆S° to be greater than, less than, or equal to 0. Explain your answer.

(d)

views

Textbook Question

Draw a reaction coordinate diagram for a one step reaction that has the following values of E_a and ∆H. (c) E_a = 5 kcal/mol; ∆H° = 0 kcal/mol

views