Atomic hydrogen (H) is used in welding (AHW). The atoms recombine to hydrogen molecules with a large release of heat according to the following reaction: 2 H1g2 → H21g2 (b) Which has the higher enthalpy under these conditions, 2 H1g2 or H21g2?

Verified step by step guidance

1. Identify the reaction: 2 \text{H}(g) \rightarrow \text{H}_2(g).
2. Understand that enthalpy (H) is a measure of the total energy of a thermodynamic system.
3. Recognize that the reaction involves the recombination of atomic hydrogen into molecular hydrogen, releasing heat.
4. Recall that exothermic reactions release heat, indicating that the products have lower enthalpy than the reactants.
5. Conclude that 2 \text{H}(g) has higher enthalpy than \text{H}_2(g) because energy is released when forming \text{H}_2(g).

Key Concepts

Enthalpy

Enthalpy is a thermodynamic property that represents the total heat content of a system. It is defined as the sum of the internal energy and the product of pressure and volume. In chemical reactions, changes in enthalpy (ΔH) indicate whether a reaction is exothermic (releases heat) or endothermic (absorbs heat). Understanding enthalpy is crucial for predicting the heat changes associated with chemical reactions.

Exothermic Reactions

Exothermic reactions are chemical processes that release energy, usually in the form of heat, to the surroundings. In the given reaction, the formation of hydrogen molecules from atomic hydrogen is exothermic, meaning that the products (H2) have lower energy than the reactants (2 H). This release of energy is a key factor in determining the enthalpy of the reactants and products.

Molecular vs. Atomic Hydrogen

Molecular hydrogen (H2) consists of two hydrogen atoms bonded together, while atomic hydrogen (H) refers to individual hydrogen atoms. The stability and energy content of these forms differ significantly; molecular hydrogen is more stable and has lower energy than atomic hydrogen. This difference is essential for understanding the enthalpy changes during the reaction, as the formation of H2 from H releases energy, indicating that H2 has a lower enthalpy than 2 H.