InterviewSolution
| 1. |
(a) Define Gibbs energy. Give its mathematical expression. What is Gibb's energy criteria of spontaneity?(b) Predict the sign of AS for the following changes:(i) Freezing of water(ii) C(graphite) → C(diamond) |
|
Answer» (a) Gibbs Energy: It is defined as the maximum amount of energy available to a system, during a process that can be converted into useful work. Mathematical Expression of Gibbs Energy: Gibbs energy is mathematically expressed as: G = H – TS Where G = Gibbs energy H = enthalpy of system S = entropy of system T = absolute temperature Change in free energy (ΔG) for the system: ΔG = ΔΗ – TΔS Where ΔΗ = change in enthalpy ΔS = change in entropy Gibbs Energy Criteria of Spontaneity: For a spontaneous reaction, ΔG is negative i.e. ΔG < 0 (b) (i) Freezing of Water: Here, entropy decreases (i.e. ΔS = −ve) because when liquid (water) freezes to form solid (ice), the molecules attain an ordered state. (ii) C(graphite) → C(diamond) Here, Entropy decreases (i.e. ΔS = −ve) because when C(graphite) is converted into C(diamond) , it attains more ordered state due to presence of covalent bonding in diamond. |
|