Use the data in Appendix B to tell which of the following compounds are thermodynamically stable with respect to their constituent elements at 25 °C: (a) BaCO3(s) (b) HBr(g) (c) N2O(g) (d) C2H4(g).

Verified step by step guidance

1. Step 1: Understand the concept of thermodynamic stability. A compound is thermodynamically stable with respect to its constituent elements if its standard Gibbs free energy of formation (ΔG_f^°) is negative at 25 °C.
2. Step 2: Locate the standard Gibbs free energy of formation (ΔG_f^°) values for each compound from Appendix B. These values are typically given in units of kJ/mol.
3. Step 3: For each compound, check the sign of the ΔG_f^° value. If ΔG_f^° is negative, the compound is thermodynamically stable with respect to its constituent elements at 25 °C.
4. Step 4: Analyze the data for each compound: (a) BaCO3(s), (b) HBr(g), (c) N2O(g), and (d) C2H4(g). Compare their ΔG_f^° values to determine their stability.
5. Step 5: Conclude which compounds are thermodynamically stable by identifying those with negative ΔG_f^° values.

Key Concepts

Thermodynamic Stability

Thermodynamic stability refers to the condition of a compound being at a lower energy state compared to its constituent elements under specified conditions, such as temperature and pressure. A thermodynamically stable compound will not spontaneously decompose into its elements, indicating that the formation of the compound is favored energetically.

Standard State and Standard Enthalpy of Formation

The standard state of a substance is its most stable form at 1 bar of pressure and a specified temperature, typically 25 °C. The standard enthalpy of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. This value helps determine the stability of a compound by comparing the energy of the compound to the energy of its constituent elements.

Gibbs Free Energy

Gibbs free energy (G) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. A negative change in Gibbs free energy (ΔG) during a reaction indicates that the products are more stable than the reactants, thus favoring the formation of the compound from its elements.