Problem 28 - Chemistry The Central Science

Question

For each of the following processes, does the potential energy of the object(s) increase or decrease? (a) The distance between two oppositely charged particles is increased. (b) Water is pumped from ground level to the reservoir of a water tower 30 \(\mathrm{m}\) above the ground. (c) The bond in a chlorine molecule, \(\mathrm{Cl}_{2},\) is broken to form two chlorine atoms.

Step-by-Step Solution

Answer

(a) The potential energy of the oppositely charged particles increases when their distance is increased. (b) The potential energy of the water increases when it is pumped to the water tower 30 m above the ground. (c) The potential energy of the chlorine molecule increases when the bond is broken to form two chlorine atoms.

Step 1: Process (a) - Oppositely charged particles

When the distance between two oppositely charged particles increases in a system, the electrostatic potential energy of the system increases. This is because the electrostatic potential energy between two charged particles is given by the formula: \[U = k \frac{q_1q_2}{r}\] Where k is Coulomb's constant, q1 and q2 are the magnitudes of the charges, and r is the distance between the charges. As the distance is in the denominator, when the distance increases, the potential energy increases.

Step 2: Answer for Process (a)

The potential energy of the oppositely charged particles increases when their distance is increased.

Step 3: Process (b) - Water pumped to a water tower

In this process, water is pumped from ground level to the reservoir in a water tower 30 m above the ground. When the water is raised to a higher level, the gravitational potential energy increases. The gravitational potential energy is given by the formula: \[U = mgh\] Where m is the mass of the water, g is the acceleration due to gravity, and h is the height above the ground. As the height, h increases, the potential energy increases.

Step 4: Answer for Process (b)

The potential energy of the water increases when it is pumped to the water tower 30 m above the ground.

Step 5: Process (c) - Chlorine molecule bond broken

In this process, a bond in a chlorine molecule (Cl₂) is broken to form two separate chlorine atoms. Breaking a bond requires energy input, which means that the potential energy stored in the chemical bond increases once the bond is broken.

Step 6: Answer for Process (c)

The potential energy of the chlorine molecule increases when the bond is broken to form two chlorine atoms.

Key Concepts

Understanding Electrostatic Potential Energy

When we consider electrostatic potential energy, we're delving into the energy stored due to the positions of charged particles in an electric field. A fundamental aspect often overlooked is that this type of potential energy stems from the force exerted by one charged particle onto another.

Take, for instance, two oppositely charged particles: as they move further apart, their mutual attraction decreases. To distance these particles, work must be done against the electric force of attraction. This work gets stored as electrostatic potential energy within the system. It is crucial to remember the formula for this energy: \[U = k \frac{q_1q_2}{r}\]where 'k' is Coulomb's constant, and 'r' represents the distance between the charges. As 'r' increases, so does the value of 'U', indicating an increase in potential energy.

Understanding this concept doesn't just apply to theoretical exercises but also explains phenomena in real-world applications, such as the energy stored in capacitors or the forces at play in the microscopic world of atoms and molecules.

Gravitational Potential Energy Explained

Moving onto gravitational potential energy, it's all about the position of an object in a gravitational field—typically, how high above the ground it is situated. This energy is a form of potential energy associated with an object due to Earth's gravity.

Similar to electrostatic potential energy, the work done to raise an object against the gravitational force is stored as gravitational potential energy. The formula here is \[U = mgh\]with 'm' being the mass of the object, 'g' the acceleration due to gravity (around 9.8 m/s² on Earth), and 'h' the height above the ground. As you pump water to the top of a water tower, the increase in height 'h' directly translates to an increase in 'U', the gravitational potential energy.

This concept is vital in areas such as civil engineering and energy production—think of pumped-storage hydroelectric stations where the gravitational potential energy of water is an essential component of electricity generation.

Chemical Bond Energy: A Close Look

Finally, when addressing chemical bond energy, we're referring to the potential energy that holds atoms together in molecules. It's the glue of the molecular world, so to speak. A chemical bond forms when atoms share or transfer electrons, releasing energy and creating a stable arrangement of atoms. Conversely, breaking a chemical bond, as in the case of a chlorine molecule (\(\text{Cl}_2\)), requires an input of energy.

The breaking of a bond in a chemical reaction involves adding energy to the system, resulting in an increase in potential energy. When the bonds of the chlorine molecule are broken to form individual chlorine atoms, the stored chemical potential energy in the bonds is released. Understanding this energy is not only crucial for exercises and academic knowledge but also plays a pivotal role in fields such as chemistry and biochemistry, impacting everything from the way medicines are designed to the energy pathways in living organisms.