Question

How is average bond strength related to relative potential energies of the reactants and the products?

Short answer

The average bond strength is directly related to the potential energy in molecules. Stronger bonds possess more potential energy since more energy is required to break them apart. When bonds in reactants are broken and new bonds are formed in products during a chemical reaction, the difference in potential energy determines if the reaction is endothermic or exothermic. In endothermic reactions, the products have a higher average bond strength and higher potential energy. In exothermic reactions, the products have a lower average bond strength and lower potential energy, resulting in energy released to the surroundings.

Step-by-step solution

Define Average Bond Strength

Average bond strength refers to the strength of a chemical bond between two atoms, typically measured in units of energy such as joules per mole (J/mol) or kilojoules per mole (kJ/mol). It represents the amount of energy required to break a bond between the atoms, or the amount of energy released when the bond is formed.

Define Potential Energy

Potential energy is the stored energy an object possesses due to its position or configuration. In the context of chemical reactions, potential energy refers to the energy stored in chemical bonds. The potential energy of a molecule depends on its structure and the strength of its chemical bonds.

Explain the Relationship between Bond Strength and Potential Energy

There is a direct relationship between bond strength and potential energy in molecules. Stronger bonds possess more potential energy since it takes more energy to break them apart. Conversely, when strong bonds are formed during a chemical reaction, more energy is released, reducing the potential energy of the molecule.

Discuss the Energy Balance in a Chemical Reaction

In a chemical reaction, bonds between atoms in the reactants are broken and new bonds are formed between the atoms in the products. The difference in potential energy between the reactants and the products determines whether the reaction is endothermic or exothermic. An endothermic reaction has a positive change in potential energy, meaning the potential energy of the products is greater than that of the reactants. In such reactions, the average bond strength of the products is higher, and energy is absorbed from the surroundings to break the bonds. An exothermic reaction has a negative change in potential energy, meaning the potential energy of the products is less than that of the reactants. In such reactions, the average bond strength of the products is lower, and energy is released to the surroundings when new bonds are formed.

Apply Concepts to a Specific Reaction

Consider a simple reaction of hydrogen gas (H2) and oxygen gas (O2) combining to form water (H2O): H2 + 0.5 O2 -> H2O In this reaction, a bond within the hydrogen molecule (H-H) is broken, as well as a bond within the oxygen molecule (O=O). Two new bonds are formed between hydrogen and oxygen atoms in the product, water (2 H-O bonds). 1. The bond strength of H-H is roughly 436 kJ/mol, which translates to a certain potential energy for H2 molecules. 2. The bond strength of O=O is around 498 kJ/mol, which corresponds to the potential energy for O2 molecules. 3. The bond strength of H-O in the product water is approximately 467 kJ/mol, translating to the potential energy of H2O molecules. 4. The energy difference between the reactants and the products is (436 + 0.5 * 498) - (2 * 467) = -242 kJ/mol. As the energy difference is negative, energy is released during the formation of water, and the reaction is exothermic. The average bond strength of the reactants is (436 + 0.5 * 498) kJ/mol. In contrast, the average bond strength of the products is 2 * 467 kJ/mol. As the average bond strength of the products is lower, this correlates with the observation that the reaction is exothermic and releases energy.