Question

9 Internal energy, enthalpy, Helmholtz ene rgy and Gibbs enthalpy are all measured in Joules a) What is the difference between these forms of energy? Give equations relating them. b) Consider a ladle containing 1 mol of molten lead at 400°C and atmospheric pressure [4] (po 101.3 kPa). The sample is left to cool very slowly to 100°C i) Split the process into three characteristic steps, stating the thermodynamic pro- [3] 13] iv) How does the internal energy of the sample change during the entire process? [3] v) How does the entropy of the sample change during the entire process? Consider [3] cess representing each step ii) Calculate the heat released during each of the steps. iii) Calculate the work done during each of the steps. Consider the direction in which heat and work flows the sign of the entropy change of the metal Thermodynamic data of lead Melting point: Tm=327°C Heat capacities: 26.7Jmol(solid) Latent heat of fusion: Lm-4.77 kJ mol- Volumetric expansion coefficient: α= 84× 10 6 K- Molar mass: M 207 g mol Densities: ps 11.34gcm-3 (solid), p 10.65gcm-3 (liquid) Assumptions vou may make Heat capacities of each phase to be independent of temperature Thermal expansion of both phases to be the same Please check the units in your calculations carefully , 30.2JmoK1 (liquid)

Answer 1

The internal energy can be either potential energy or kinetic energy. The main difference between enthalpy and internal energy is that enthalpy is the heat absorbed or evolved during chemical reactions that occur in a system whereas internal energy is the sum of potential and kinetic energy in a system.