Question

Which of the following is a violation of the law of conservation of energy" A. Heat can be changed completely to work in cyclical process. B. A system undergoing a reaction with constant enthalpy experiences a temperature change. C. After sliding to a stop, a box with initial kinetic energy \(K\) has only thermal energy in an amount less than \(K\). D. A bond is broken and energy is released,

Short answer

C

Step-by-step solution

Identify the Law of Conservation of Energy

The law of conservation of energy states that energy cannot be created or destroyed, but can only be transformed from one form to another. The total energy in an isolated system remains constant over time.

Analyze Option A

Option A states that heat can be changed completely to work in a cyclical process, which violates the second law of thermodynamics rather than the law of conservation of energy, because it implies 100% efficiency in conversion.

Analyze Option B

Option B indicates that a system can undergo a reaction with constant enthalpy and experience a temperature change. This does not violate the conservation of energy, as energy can be redistributed within the system to change the temperature.

Analyze Option C

Option C describes a box with initial kinetic energy sliding to a stop and having thermal energy less than the initial kinetic energy. This suggests some energy is lost, which violates the law of conservation of energy, since energy cannot simply disappear.

Analyze Option D

Option D explains that energy is released when a bond is broken. This complies with the conservation of energy, as the energy released comes from the bond's stored potential energy that is converted to other forms.

Conclude the Correct Answer

Based on the analyses, Option C is the one that violates the law of conservation of energy, as it implies energy loss without an account of the transformation to another form.

Key concepts

Thermodynamics

Thermodynamics is the branch of physical science that deals with the relationships between heat and other forms of energy. It describes how energy moves and changes in form. There are several laws of thermodynamics, which help us understand everything from the behavior of atoms to the engines in our cars.

• The first law is the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed.
• The second law states that the total entropy of an isolated system can never decrease over time. This means energy transformations are not 100% efficient.
• The third law states that as temperature approaches absolute zero, the entropy of a system approaches a minimum.

Enthalpy

Enthalpy is a measure of the total heat content of a system. It's a thermodynamic quantity equivalent to the total heat content of a system and is used to quantify the heat changes at constant pressure. The symbol for enthalpy is H.
When we talk about constant enthalpy, it means that the heat transferred to or from the system does not change its temperature, but rather the internal energy or work done by the system. For example, in the case of chemical reactions, the energy absorbed or released might not change the temperature because it's used in forming or breaking bonds.

Kinetic Energy

Kinetic energy is the energy that an object possesses due to its motion. The amount of kinetic energy (KE) depends on the mass and velocity of the object. The formula for kinetic energy is: \[ KE = \frac{1}{2} mv^2 \] where:

• m represents the mass of the object
• v represents the velocity of the object

When an object like a sliding box slows to a stop, it doesn't lose energy. Instead, this energy transforms into thermal energy due to friction. If the final thermal energy is less than the initial kinetic energy, it suggests some energy is missing, which would violate the conservation of energy principle.

Energy Transformation

Energy transformation refers to the process of changing energy from one form to another. For example, when you eat food, your body transforms the chemical energy in food into mechanical energy and heat energy. According to the law of conservation of energy, energy transformations never result in a net loss or gain of energy.
Key points about energy transformation include:

• Energy can change forms, such as from kinetic energy to potential energy, but the total amount of energy remains constant.
• In real-world applications, some energy is often lost as heat due to inefficiencies in the system.
• Examples include potential energy transforming into kinetic energy, chemical energy transforming into electrical energy, etc.