Basic Thermochemistry in Materials Processing by Gabriel Plascencia, David Jaramillo

By Gabriel Plascencia, David Jaramillo

This publication presents the reader with a few thermochemistry notes. The goal is to supply an easy, effortless to appreciate textual content which serves as a complimentary fabric to extra advanced books. It additionally supply scholars and people starting within the box with a number of software examples utilized in assorted components of fabrics processing. The e-book offers totally solved difficulties, a few usually present in significant metallurgical operations.

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Why not the common temperature of the moles is 50 °C? How much heat is transferred? The heat capacity of gold is: CpAu ¼ 23:7 þ 5:19 Â 10À3 T J=mol=K Repeat the calculations if cobalt or magnesium is used instead of gold, using the following data: 0:88 Â 105 J=mol=K T2 4:31 Â 104 ¼ 22:3 þ 1:03 Â 10À2 T À J=mol=K T2 CpCo ¼ 21:4 þ 1:43 Â 10À2 T À CpMg Solution The energy balance establishes that qtotal = qhot + qcold = 0. The energy exchange has to be expressed in terms of the Cp of the metal: Energy Balance: qnet ¼ DHtotal ¼ DHAu;hot þ DHAu;cold ¼ 0 ZT DHAu;hot ¼ ZT À CpAu dT ¼ 373 Á 23:7 þ 5:19 Â 10À3 T dT 373 À Á DHAu;hot ¼ 23:7ðT À 373Þ þ 2:6 Â 10À3 T 2 À 3732 similarly for the cold gold ZT DHAu;cold ¼ ZT CpAu dT ¼ 273 À Á 23:7 þ 5:19 Â 10À3 T dT 273 À Á DHAu;cold ¼ 23:7ðT À 273Þ þ 2:6 Â 10À3 T 2 À 2732 adding DHAu;cold to DHAu;hot À Á À Á qnet ¼ 23:7ðT À 373Þ þ 2:6 Â 10À3 T 2 À 3732 þ 23:7ðT À 273Þ þ 2:6 Â 10À3 T 2 À 2732 qnet ¼ 47:4T þ 5:19 Â 10À3 T 2 À 15; 865:7 ¼ 0 solving for T T ¼ 323:27 K; T ¼ 50:27  C Examples of Calculations 23 Since Cp increases with T, the temperature change caused by adding heat to the system is imposed over that withdrawing it.

As temperature increases, the entropy contribution to DG becomes more important. Furthermore if we follow phase transitions as more energy is supplied to any system, we can easily observe the change of entropy as a solid transforms into a liquid and the liquid boils into a gas. Not surprisingly, the entropy of each phase progressively increases from the solid to the gaseous state; this can be seen in Fig. 4. 4 show the effect of enthalpy and entropy, respectively, on Gibbs free energy during phase transitions.

5. 11) can also be integrated between limits P1 and P2 corresponding to T1 and T2, respectively; if such is the case, Eq. 12) results in:  ln P2 P1    DH 1 1 À ¼À : R T2 T1 ð2:13Þ This last expression is the integrated form of Clausius–Clapeyron equation. 13) is often used to estimate the vapor pressures of pure liquids or solids. DH is the enthalpy of vaporization if the substance is a liquid or the enthalpy of sublimation if it is a solid. The enthalpy of vaporization (or sublimation) is assumed to be constant over the temperature range of interest.

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