91Ó°ÊÓ

Commercial cold packs often contain solid \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) and a pouch of water. The temperature of the pack drops as the \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) dissolves in water. Therefore, for the dissolving of \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) in water, a. \(\Delta \mathrm{H}_{\mathrm{soln}}\) is positive and \(\Delta \mathrm{S}_{\text {soln }}\) is positive. b. \(\Delta \mathrm{H}_{s \mathrm{son}}\) is positive and \(\Delta \mathrm{S}_{\text {soln }}\) may be negative or positive c. \(\Delta \mathrm{H}_{\text {slin }}\) is negative and \(\Delta \mathrm{S}_{\text {spln }}\) may be negative or positive d. \(\Delta \mathrm{H}_{\mathrm{seln}}\) is negative and \(\Delta \mathrm{S}_{\mathrm{soln}}\) is positive

Step by step solution

01

Understand the process

When ammonium nitrate, \(\mathrm{NH}_{4} \mathrm{NO}_{3}\), dissolves in water, it absorbs heat from the surroundings, which is why the solution gets cold. This indicates that the process is endothermic.

02

Determine the sign of \(\Delta \mathrm{H}_{\mathrm{soln}}\)

Since the dissolution of \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) absorbs heat, the enthalpy change, \(\Delta \mathrm{H}_{\mathrm{soln}}\), is positive.

03

Consider the entropy change \(\Delta \mathrm{S}_{\mathrm{soln}}\)

Dissolving a solid into a liquid increases the disorder of the system because the ions from the solid are now moving freely in the solution, leading to an increase in entropy. Thus, \(\Delta \mathrm{S}_{\mathrm{soln}}\) is positive.

04

Identify the correct option

Given that \(\Delta \mathrm{H}_{\mathrm{soln}}\) is positive and \(\Delta \mathrm{S}_{\mathrm{soln}}\) is positive, the correct choice is option (a).

Unlock Step-by-Step Solutions & Ace Your Exams!

• Full Textbook Solutions

  Get detailed explanations and key concepts

• Unlimited Al creation

  Al flashcards, explanations, exams and more...

• Ads-free access

  To over 500 millions flashcards

• Money-back guarantee

  We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Endothermic process

When a reaction or process absorbs heat from its surroundings, it is described as an endothermic process. This is easily observed in a commercial cold pack, where solid ammonium nitrate (\(\mathrm{NH}_{4} \mathrm{NO}_{3}\)) dissolves in water, leading to the absorption of heat. As the cold pack becomes cooler, it signifies that energy has been taken from the surrounding environment, specifically in the form of heat.

Endothermic processes are characterized by the following:

• Absorption of energy: The system gains energy from the surroundings, resulting in a decrease in temperature of the immediate environment.
• Positive energy change: The energy absorbed is represented by a positive value in energy changes.
• Typical applications: Endothermic processes are not just limited to cold packs but are also found in biological systems during processes such as photosynthesis.

Understanding endothermic processes helps us comprehend how matter interacts with energy on a molecular level, thereby impacting both natural and manmade systems.

Enthalpy change

Enthalpy change, often represented as \(\Delta H\), is a measure of heat absorbed or released during a chemical reaction or process. It is a key concept in thermodynamics and helps us understand how reactions work on an energetic level.

For the specific case of dissolving ammonium nitrate in water:

• Positive \(\Delta H\): Since the process absorbs heat, the enthalpy change is positive, indicating that the system requires energy input to proceed.
• Relation to temperature: A positive \(\Delta H\) typically leads to a decrease in temperature, as the system absorbs heat from its surroundings.
• Interpreting \(\Delta H\) values: Enthalpy changes provide insight into the energy needs or outputs of chemical reactions, assisting in industrial and laboratory applications to control reaction environments.

Appreciating the enthalpy changes in solution processes allows chemists to predict reaction behavior, design better industrial processes, and exploit chemical reactions for practical uses.

Entropy change

Entropy, symbolized as \(\Delta S\), measures the degree of disorder or randomness in a system. When a solid substance like ammonium nitrate dissolves in water, this disorder generally increases, leading to an increase in entropy.

For the dissolution of ammonium nitrate:

• Positive \(\Delta S\): The increase in entropy reflects the greater movement freedom now available to particles in a solution compared to their ordered solid-state.
• Disorder and spontaneity: Processes that increase disorder (positive \(\Delta S\)) are often spontaneous or favorable without any added energy.
• Combining \(\Delta S\) with \(\Delta H\): Understanding both these changes together through Gibbs Free Energy (\(\Delta G = \Delta H - T\Delta S\)) helps predict whether a reaction will occur under particular conditions.

By considering entropy changes, chemists gain a deeper insight into the nature of chemical reactions and the factors that drive them, aiding in the exploration and utilization of new materials and reactions.