Without referring to tables, predict which of the following has the higher enthalpy in each case: (b) 2 mol of iodine atoms or 1 mol of I₂

Verified step by step guidance

1. Understand the concept of enthalpy, which is a measure of the total energy of a thermodynamic system, usually expressed in joules or kilojoules per mole.
2. Recognize that the enthalpy of a substance depends on its molecular structure and the bonds between atoms. Stronger bonds generally mean lower enthalpy.
3. Consider the molecular structure of iodine in its different forms: as individual iodine atoms and as I₂ molecules. I₂ consists of two iodine atoms bonded together.
4. Recall that forming a bond releases energy, thus stabilizing the system. Therefore, a molecule of I₂, which has a covalent bond between two iodine atoms, would have a lower enthalpy compared to separate iodine atoms which have no bonds.
5. Conclude that 1 mol of I₂ would generally have a lower enthalpy than 2 mol of iodine atoms, because the bonded I₂ molecules are in a lower energy state compared to separate atoms.

Key Concepts

Enthalpy

Enthalpy is a thermodynamic quantity that represents the total heat content of a system. It is defined as the internal energy of the system plus the product of its pressure and volume. Enthalpy changes are crucial in chemical reactions, as they indicate whether a reaction is exothermic (releases heat) or endothermic (absorbs heat). Understanding enthalpy helps predict the stability and reactivity of substances.

Diatomic Molecules

Diatomic molecules consist of two atoms, which can be of the same or different elements. In the case of iodine, I2 is a diatomic molecule made up of two iodine atoms bonded together. The formation of a diatomic molecule from individual atoms typically involves a release of energy, resulting in a lower enthalpy for the molecule compared to its constituent atoms. This concept is essential for comparing the enthalpy of I2 and free iodine atoms.

Bond Energy

Bond energy is the amount of energy required to break a bond between two atoms in a molecule. In the context of I2, the bond energy reflects the stability of the I-I bond. When comparing 2 mol of iodine atoms to 1 mol of I2, the bond energy indicates that breaking the I-I bond in I2 requires energy, thus making I2 lower in enthalpy than the separate iodine atoms. This concept is key to understanding the energy changes involved in molecular formation.