Ch.9 - Thermochemistry: Chemical Energy

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.9 - Thermochemistry: Chemical Energy

Problem 6a

Chapter 9, Problem 6a

Several processes are given in the table and labeled as endo- thermic or exothermic and given a sign for ∆H°. Which process is labeled with the correct sign of ∆H° and correct classification as endothermic or exothermic? (LO 9.8) Process (a) Ammonium nitrate dissolves in water, and the temperature of the solution decreases.

Verified step by step guidance

Identify the nature of the process: When ammonium nitrate dissolves in water and the temperature of the solution decreases, it indicates that the system is absorbing heat from the surroundings. This is a key characteristic of an endothermic reaction.

Understand the sign of ∆H°: For endothermic processes, the enthalpy change (∆H°) is positive. This is because the system gains heat, increasing its enthalpy.

Check the given classification and sign: The process should be labeled as endothermic with a positive ∆H°.

Compare with the problem statement: Ensure that the process of ammonium nitrate dissolving in water is correctly labeled as endothermic and that the sign of ∆H° is positive.

Conclude the correctness: If the process is labeled as endothermic and the sign of ∆H° is positive, then it is correctly classified and labeled.

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Key Concepts

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

Endothermic and Exothermic Reactions

Endothermic reactions absorb heat from their surroundings, resulting in a decrease in temperature, while exothermic reactions release heat, causing an increase in temperature. The sign of the enthalpy change (∆H°) reflects this: positive for endothermic processes and negative for exothermic ones.

Enthalpy Change (∆H°)

Enthalpy change (∆H°) is a measure of the heat content of a system at constant pressure. It indicates whether a process is endothermic or exothermic. A positive ∆H° signifies that heat is absorbed (endothermic), while a negative ∆H° indicates that heat is released (exothermic).

Dissolution Process

The dissolution process involves a solute (like ammonium nitrate) dissolving in a solvent (like water). This process can be endothermic if it requires energy to break solute-solute and solvent-solvent interactions, leading to a decrease in the solution's temperature, which is observed when ammonium nitrate dissolves.

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Textbook Question

Several processes are given in the table and labeled as endo- thermic or exothermic and given a sign for ∆H°. Which process is labeled with the correct sign of ∆H° and correct classification as endothermic or exothermic? (LO 9.8) Process (c) Water freezes into ice in the freezer.

For which of the following reactions are ΔE and ΔH equal? (a) CO2(g) + H2O(l) → H2CO(b) 2 NaHCO3 (s) → Na2CO3(s) + H2O(g) + CO2(g)(c) 2 H2(g) + O2(g) → 2 H2O(g)(d) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)

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Textbook Question

A room-temperature balloon filled with air is placed in the freezer and the balloon contracts. What is the sign of q and w for the air inside the balloon? (LO 9.4)(a) q = +, w = - (b) q = +, w = + (c) q = -, w = - (d) q = -, w = +

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