In energy changes during chemical reactions, when a chemical bond is broken, what happens to energy?

Introduction / Context:
Understanding how energy changes during chemical reactions is essential for studying thermochemistry. One key idea is that breaking chemical bonds and forming new bonds involve energy changes. It is a common misconception that breaking bonds always releases energy. In reality, energy must be supplied to break existing bonds, while energy is released when new bonds form. This question focuses specifically on what happens to energy when a chemical bond is broken.

Given Data / Assumptions:
- We consider ordinary chemical bonds such as covalent bonds in molecules. - Bond breaking involves separating bonded atoms into individual atoms or ions. - We are looking at the direction of energy flow between the system and the surroundings. - We assume standard conditions and typical classroom examples of reactions.

Concept / Approach:
Chemical bonds represent stable arrangements of electrons between atoms. To break a bond, the system must overcome the attractive forces holding the atoms together. This requires an input of energy from the surroundings, meaning bond breaking is an endothermic process. The energy absorbed is called bond energy or bond dissociation energy. In contrast, when new bonds form, energy is released to the surroundings, making bond formation exothermic. The overall energy change of a reaction depends on the balance between energy absorbed in bond breaking and energy released in bond formation.

Step-by-Step Solution:
Step 1: Consider a simple diatomic molecule such as H2. The H H bond holds the two hydrogen atoms together. Step 2: To break the H H bond and separate the atoms, we must supply energy to the molecule, for example by heating or using light. Step 3: This supplied energy goes into overcoming the attractive forces, so it is said that energy is absorbed or used by the system. Step 4: This idea is captured in the definition of bond dissociation energy, which is always a positive quantity representing the energy required to break a bond. Step 5: Therefore, when a chemical bond is broken, the process is endothermic and energy is taken in from the surroundings. Step 6: From the options, the statement that energy is used or absorbed to break the bond is the best description.

Verification / Alternative check:
You can verify this principle by looking at energy level diagrams for reactions. When bonds in reactants are broken, the potential energy of the system increases. Only after new bonds form does the potential energy decrease, releasing energy as heat or light. Textbook examples of bond energies always show that energy values for breaking bonds are positive (energy in), while formation of the same bonds would have negative energy values of the same magnitude (energy out). This consistent pattern confirms that breaking bonds uses or absorbs energy.

Why Other Options Are Wrong:
Option A suggests that energy is transferred into the bond without being used, which is unclear and does not match the idea that the energy input is required to overcome attractive forces. Option B states that energy is released in all cases when a bond is broken, which reverses the actual situation; bond breaking is not exothermic. Option D claims that none of the options are correct, which is wrong because Option C accurately states that energy is used or absorbed in bond breaking.

Common Pitfalls:
A very common misconception is that breaking bonds releases energy because students often hear that energy is stored in bonds. In reality, it is the formation of stronger, more stable bonds in the products that releases energy. Another pitfall is to focus only on the overall reaction energy and not distinguish between individual steps of bond breaking and bond forming. To avoid confusion, remember the rule: breaking bonds requires energy input, while forming bonds releases energy.

Final Answer:
The correct answer is: Energy is used or absorbed from the surroundings to break the bond.