A state function defined by G = H − TS. At constant temperature and pressure, changes proceed spontaneously in the direction that lowers G, and the state of minimum G is equilibrium.
Japanese name: ギブスエネルギー
Gibbs energy appears in 6 practice questions across 3 topics, including Thermodynamics of materials, Computational materials science, Battery and energy materials.
Field: Thermodynamics of materials
Answer: B. About 1.23 V
The theoretical emf is E = −ΔG/(nF), and when 1 mol of H₂ reacts, 2 mol of electrons are transferred, so n = 2. E = 237×10³ / (2 × 96485) ≈ 1.23 V. About 2.46 V takes n = 1, and about 0.61 V combines the number of electrons per mole of O₂, n = 4, with ΔG per mole of H₂. The ratio of the Gibbs energy change to the enthalpy change of the reaction (−286 kJ/mol), 237/286 ≈ 83%, is a guide to the theoretical efficiency at 25 °C. In real cells, electrode overpotentials and electrolyte resistance lower the operating voltage to about 0.6–0.8 V.
Answer: A. It is negative at all compositions and its slope tends to minus infinity as x → 0, so a tiny amount of solute dissolves in any substance
In an ideal solution the enthalpy of mixing is 0, and ΔG_mix = −TΔS_mix arises only from the entropy of mixing. For 0 < x < 1, ln x is negative, so ΔG_mix is negative at all compositions and takes its minimum value RT ln 0.5 at x = 0.5 (about −5.76 kJ/mol at 1000 K). As x → 0, the slope d(ΔG_mix)/dx = RT ln[x/(1 − x)] tends to minus infinity, so dissolving even a tiny amount of solute always lowers the free energy. This is the thermodynamic reason why it is difficult to make a perfectly pure substance. ΔG_mix is proportional to T and has nothing to do with enthalpy. What is largest at x = 0.5 is the entropy of mixing; ΔG_mix is at its minimum there.
The ratio of the Gibbs energy change to the enthalpy change of the reaction (−286 kJ/mol), 237/286 ≈ 83%, is a guide to the theoretical efficiency at 25 °C.
The standard Gibbs energy change of the reaction forming li…At constant temperature and pressure, a change proceeds spontaneously in the direction that lowers the Gibbs energy of the system, G = H − TS (ΔG < 0), and equilibrium is reached at ΔG = 0.
At constant temperature and pressure, which quantity and co…When the molar Gibbs energy is plotted against composition, this corresponds to drawing a tangent common to the 2 curves, and the 2 points of tangency give the compositions of the 2 phases in equilibrium.
At constant temperature and pressure, which is the correct …In the CALPHAD (CALculation of PHAse Diagrams) method, the Gibbs energy of each phase, such as liquid, solid solutions and compounds, is expressed as the sum of pure-substance terms, an ideal mixing term and an excess term representing interactions.
Which statement about the CALPHAD method is correct?Experimenting at every composition of a multicomponent system is impossible, but with Gibbs energy models, parameters determined for binary and ternary systems can be combined to extrapolate to the multicomponent system.
The CALPHAD method is used to predict the precipitating pha…CALPHAD method Entropy of mixing Density functional theory Nickel-based superalloy Activity Chemical potential Ellingham diagram Equilibrium oxygen partial pressure Regular solution Spinodal decomposition