Pertemuan_3_Prinsip Termodinamika dan Diagram Fasa.pptx

Prinsip Termodinamika dan Diagram Fasa

1. TRANSFORMASI FASA MM201436 Kelas A 3 SKS Pertemuan 3 Oleh Andromeda Dwi Laksono, ST, MSc Program Studi Teknik Material dan Metalurgi Jurusan Ilmu Kebumian dan Lingkungan ITK 20 20

2. Kesetimbangan , termodinamika dan diagram Fasa Pengertian dan Konsep Keseimbangan Kesetimbangan menyebabkan komposisi , temperatur , tekanan dan kondisi lain yang mempengaruhi suatu sistem berada pada energi terendah Sistem bahan tidak murni , terdapat impuritas atau bahan tambahan yang hasilnya merupakan larutan padat , multi kristalin , campuran kristalin atau campuran kristalin-nonkristalin

3. equilibrium It is useful to begin by defining a few of the terms that will be frequently used. - system - phase - component The study of phase transformations, as the name suggest, is concerned with how one or more phases in an alloy (the system) change into a new phase or mixture phases. For transformation that occur at constant temperature and pressure the relative stability of a system is determined by its Gibbs free energy (G) G = H – TS H : enthalpy, T : absolute temperature, S : entropy

4. Enthalpy is measure of the heat content of the system H = E + PV Where E : internal energy of system P : pressure V : volume The internal energy arises from the total kinetic and potensial energy Kinetic energy can arise from atomic vibration in solid or liquid and from translational and rotational energies for the atoms or molecules within a liquid or gas Potential energy arises from the interaction, or bond between the atoms within the system

5. If a transformation or reaction occurs the heat that is absorbed or envolved will depend on the change in the internal energy of the system. When dealing with condensed phases ( solids and liquids) the PV term is ussualy very small in comparison to E, that is H ≈ E The other function that appears in the expression for G is entropy (S) which is a measure of the randomness of the system A system is said to be in equilibrium when it is in the most stable state An important consequence of the law of classical thermodynamics is that at constant T and P a closed system will be in stable equilibrium if it has the lowest G or dG = 0

6. Equilibrium A mechanical analogy for chemical change is that of a ball rolling down a slope with multiple valleys; we explain the ball's behavior by saying that mechanical systems have a tendency to reduce their potential energy.  At  equilibrium  none of the properties of a system change with time. A system at equilibrium returns to equilibrium if disturbed.  " Stable " describes a system or phase in its lowest energy state.  " Metastable " describes a system or phase in any other energy state. 

7. The figure above shows the mechanical analogy for H 2 O at -5°C and + 5°C and 1 atm. Left: at -5°C, solid H 2 O has the lowest possible energy state. Right: at +5°C, liquid H 2 O has the lowest possible energy state. When solid H 2 O is actually present at +5°C, the difference between the free energy of solid H 2 O and liquid H 2 O is available to drive the reaction to form the stable solid H 2 O phase, and the reaction will go to completion if kinetically possible.

8. Hukum-hukum termodinamika Pengertian keseimbangan diberikan oleh hukum-hukum termodinamika yang dinyatakan dalam energi bebas Gibbs suatu sistem Dimana, G = energi bebas Gibbs, P = tekanan sistem, V = volume sistem, T = temperatur mutlak, S = entropi,  I = potensial kimia komponen ke-i dan X i = fraksi mol ke-i Keadaan seimbang dicapai bila harga energi bebas Gibbs G mencapai minimum

9. Bila keseimbangan dicapai , temperatur dan tekanan harus uniform dalam sistem dan potensial kimia untuk setiap komponen harus sama dalam setiap fasa yang berada dalam kesetimbangan

10. Diagram fasa sistem satu komponen Fasa yang akan terjadi adalah uap , cair dan padat beserta polimorfisme nya Variabel bebas yang dapat menghilangkan dan menimbulkan fasa adalah temperatur dan tekanan

11. Pada titik A, ketiga fasa dalam keseimbangan , setiap perubahan temperatur dan tekanan menyebabkan hilangnya satu fasa . Jumlah fasa maksimal dicapai bila variansinya sama dengan nol Pada titik B, terletak pada garis diagram, menyatakan keadaan dimana dua fasa berada dalam kesetimbangan . P = 2 dan C = 1 sehingga V = 1. hal ini berarti bahwa baik tekanan atau temperatur tetapi tidak keduanya dapat berubah secara bebas tanpa kehilangan fasa . Pada titik C, P = 1 dan C = 1 sehingga V = 2, artinya tekanan dan temperatur keduanya dapat berubah tanpa menghilangkan fasa

12. Pada tekanan rendah terdapat 5 fasa yaitu ; -quartz, -quartz,  2 -tridymite, -cristobalite dan silika cair . Pada 573°C terjadi transformasi -quartz ke -quartz secara cepat dan reversibel sedangkan transformasi fasa yang lain terjadi sangat lambat sehingga membutuhkan waktu yang panjang untuk mencapai kesetimbangan

13. 1 - C Systems 1. The system SiO 2 Fig. 6.6. After Swamy and Saxena (1994) , J. Geophys . Res., 99, 11,787-11,794 . AGU

14. Phase Rule in One-Component Systems 23 Notice that in one-component systems, the number of degrees of freedom seems to be related to the number of phases.

15. Phase Rule in One-Component Systems 24 The phase rule should be applicable for any single-component systems in general.

16. TUGAS! The specific heat of solid copper above 300 K is given by Cp = 22.64 + 6.28x10-3 T Jmol -1 K -1 by how much does the entrophy of copper increase on heating from 300 to 1358 K? Estimate the change in the equilibrium melting point of copper caused by change pressure of 10 kbar. The molar volume of copper is 8,0x10 -6 m 3 for liquid and 7,6x10 -6 for solid phase. The latent heat of fusion of copper is 13.05 kJmol -1 . the melting point is 1085 o C