When ammonium chloride (NH4 Cl) is dissolved in water, the solution becomes colder. a. Is the di

When ammonium chloride (NH4 Cl) is dissolved in water, the...

When ammonium chloride $\left(\mathrm{NH}_{4} \mathrm{Cl}\right)$ is dissolved in water, the solution becomes colder. a. Is the dissolution of ammonium chloride endothermic or exothermic? b. What can you conclude about the relative magnitudes of the lattice energy of ammonium chloride and its heat of hydration? c. Sketch a qualitative energy diagram similar to Figure $12.7$ for the dissolution of $\mathrm{NH}_{4} \mathrm{Cl}$. d. Why does the solution form? What drives the process?

When ammonium chloride $\left(\mathrm{NH}_{4} \mathrm{Cl}\right)$ is dissolved in water, the solution becomes colder.
a. Is the dissolution of ammonium chloride endothermic or exothermic?
b. What can you conclude about the relative magnitudes of the lattice energy of ammonium chloride and its heat of hydration?
c. Sketch a qualitative energy diagram similar to Figure $12.7$ for the dissolution of $\mathrm{NH}_{4} \mathrm{Cl}$.
d. Why does the solution form? What drives the process?

Key Concepts

Endothermic Processes

An endothermic process is one in which heat is absorbed from the surroundings. When a solute dissolves in a solvent and the temperature of the solution decreases, it indicates that the overall process is endothermic, meaning that the energy required to break the intermolecular forces is greater than the energy released from solvation.

Lattice Energy

Lattice energy is the energy required to separate one mole of an ionic solid into its gaseous ions. It is a measure of the strength of the forces holding the ions in the solid structure. In the context of dissolution, a high lattice energy must be overcome by the energy released during hydration of the ions.

Heat of Hydration

The heat of hydration refers to the energy released when ions are surrounded by water molecules during dissolution. This exothermic process can partially offset the energy required to break the ionic lattice, but if the hydration energy is less than the lattice energy, the overall process will absorb heat, leading to an endothermic dissolution.

Gibbs Free Energy and Spontaneity

Gibbs free energy combines enthalpy and entropy changes to determine the spontaneity of a process. Even if dissolution is endothermic (positive enthalpy change), it can still be spontaneous if the entropy change (increase in disorder) is sufficiently favorable. The overall negative Gibbs free energy drives the formation of the solution.

Energy Diagrams

Energy diagrams provide a qualitative visual representation of the energy changes during a chemical process. For dissolution, the diagram would illustrate the energy required to separate the ions from the solid (overcoming lattice energy), followed by the energy release from hydration. The difference between these energy changes reflects the net endothermic or exothermic nature of the reaction.

Transcript

00:01 In this question we're going to be looking at the dissolution of ammonium chloride.

00:06 And when we're talking about thermodynamics, there are two types of processes that is exothermic and an endothermic process.

00:18 So to describe these, these processes or this phenomenon, they are usually described in the perspective of the system and its surrounding.

00:30 So what we are looking at by the system, say, for example, right now we are trying to dissolve ammonium chloride into.

00:36 Solution so this dissolution process this solution is what we're going to call the system and this external environment is what we're going to be calling the surrounding so in terms of heat transfer and heat content when we are looking at exothermic and endothermic for an endothermic reaction or an endothermic process this system will be absorbing energy from its surroundings in such a way that at the end of the process the system is going to have a higher energy content than it did when it started so what is going to happen is because of this higher energy content there is going to be an increase in temperature of the system but since energy is being drawn from the surrounding into the process or the system the surrounding is going to have a lower temperature so chaos to be made because this is always looked from the perspective of the system and the environment.

01:39 The system will increase the temperature because it is absorbing energy from its surrounding.

01:45 So its temperature will increase.

01:47 But when we are looking at the surroundings, the surrounding temperature is going to decrease.

01:52 So looking at the dissolution of ammonium chloride, we're told that the solution is going to increase in temperature, meaning it absorbed energy from its surrounding.

02:03 Hence we call this and endothermic process and the opposite of that is the exothermic in which the system is losing energy to the surroundings so after the process is okayed for an exothermic reaction the surroundings are going to be at a higher temperature this is what we we ourselves are going to be feeling as sensible heat we're going to feel heat if we feel that heat from a system it means that system is releasing heat so it is an exothermic process but when we are looking it from within the system, it is losing the heat.

02:40 So it is going to be at a lower energy level than it was initial.

02:45 Then moving on to the other part.

02:47 Now that we know that the formation of ammonium chloride or rather ammonium chloride solution is an endothemic process.

02:54 It is an endothermic.

02:56 It is an endothermic process...

Please give Ace some feedback