The Dissolution of Sodium Hydroxide Pellets

Oct 13, 2025 by wbrum.org 71 views

Introduction

In chemistry, thermodynamic properties such as enthalpy (H), entropy (S), and Gibbs free energy (G) play a crucial role in understanding the behavior of chemical reactions. These properties can be used to predict the spontaneity, feasibility, and direction of a reaction. In this article, we will discuss the signs of ΔH, ΔS, and ΔG for the dissolution of sodium hydroxide pellets in water at room temperature.

The Dissolution of Sodium Hydroxide Pellets

Trevor dissolves sodium hydroxide pellets in a beaker of water at room temperature and notes that the beaker becomes warm. This observation suggests that the dissolution process is endothermic, meaning it absorbs heat from the surroundings. As a result, the temperature of the beaker increases.

Signs of ΔH, ΔS, and ΔG

ΔH (Enthalpy Change)

ΔH is a measure of the heat absorbed or released during a reaction. In this case, the dissolution of sodium hydroxide pellets in water is an endothermic process, meaning it absorbs heat from the surroundings. Therefore, the sign of ΔH is positive (+).

ΔS (Entropy Change)

ΔS is a measure of the disorder or randomness of a system. In this case, the dissolution of sodium hydroxide pellets in water increases the disorder of the system, as the ions and water molecules become more randomly arranged. Therefore, the sign of ΔS is positive (+).

ΔG (Gibbs Free Energy Change)

ΔG is a measure of the spontaneity of a reaction. It is related to the enthalpy and entropy changes of a reaction by the equation:

ΔG = ΔH - TΔS

In this case, the dissolution of sodium hydroxide pellets in water is an endothermic process, meaning it absorbs heat from the surroundings. However, the entropy change is also positive, indicating an increase in disorder. To determine the sign of ΔG, we need to consider the temperature of the system.

At room temperature, the entropy change (ΔS) is greater than the enthalpy change (ΔH), resulting in a negative value of ΔG. This indicates that the dissolution of sodium hydroxide pellets in water is a spontaneous process.

Conclusion

In conclusion, the dissolution of sodium hydroxide pellets in water at room temperature is an endothermic process, meaning it absorbs heat from the surroundings. The signs of ΔH, ΔS, and ΔG for this process are:

ΔH: positive (+)
ΔS: positive (+)
ΔG: negative (-)

This indicates that the dissolution of sodium hydroxide pellets in water is a spontaneous process, driven by the increase in disorder and the absorption of heat from the surroundings.

References

Atkins, P. W., & De Paula, J. (2010). Physical chemistry (9th ed.). Oxford University Press.
Chang, R. (2010). Physical chemistry for the biosciences. University Science Books.
Levine, I. N. (2012). Physical chemistry (6th ed.). McGraw-Hill.

Introduction

In our previous article, we discussed the signs of ΔH, ΔS, and ΔG for the dissolution of sodium hydroxide pellets in water at room temperature. In this article, we will answer some frequently asked questions related to thermodynamic properties in chemical reactions.

Q&A

Q: What is the difference between ΔH and ΔU?

A: ΔH (enthalpy change) and ΔU (internal energy change) are both measures of the energy change in a system. However, ΔH takes into account the energy associated with the expansion or contraction of a system, whereas ΔU does not. In general, ΔH = ΔU + Δ(PV), where Δ(PV) is the change in the product of pressure and volume.

Q: What is the relationship between ΔS and ΔG?

A: ΔS (entropy change) and ΔG (Gibbs free energy change) are related by the equation:

ΔG = ΔH - TΔS

This equation shows that ΔG is a function of both ΔH and ΔS. In general, a negative value of ΔG indicates a spontaneous process, while a positive value indicates a non-spontaneous process.

Q: What is the significance of ΔG = 0?

A: When ΔG = 0, it means that the reaction is at equilibrium, and the forward and reverse reactions occur at the same rate. This is known as a reversible reaction.

Q: Can ΔG be negative for a non-spontaneous process?

A: Yes, it is possible for ΔG to be negative for a non-spontaneous process. This occurs when the reaction is at a high temperature, and the entropy change (ΔS) is large enough to overcome the enthalpy change (ΔH).

Q: What is the relationship between ΔH and ΔS in a phase transition?

A: In a phase transition, such as the melting of ice or the vaporization of water, ΔH is typically positive, indicating an increase in energy. However, ΔS is also positive, indicating an increase in disorder. This is because the molecules become more randomly arranged in the new phase.

Q: Can ΔH be negative for a phase transition?

A: Yes, it is possible for ΔH to be negative for a phase transition. This occurs when the reaction is exothermic, meaning it releases heat to the surroundings.

Q: What is the significance of ΔS = 0?

A: When ΔS = 0, it means that the system is at a state of maximum disorder, and there is no change in entropy. This is known as a reversible process.

Conclusion

In conclusion, thermodynamic properties such as ΔH, ΔS, and ΔG play a crucial role in understanding the behavior of chemical reactions. By understanding the relationships between these properties, we can predict the spontaneity, feasibility, and direction of a reaction.

References

Atkins, P. W., & De Paula, J. (2010). Physical chemistry (9th ed.). Oxford University Press.
Chang, R. (2010). Physical chemistry for the biosciences. University Science Books.
Levine, I. N. (2012). Physical chemistry (6th ed.). McGraw-Hill.