Question

b. Manually determine the molar ∆rC°P for the reaction albite Þ jadeite + quartz at 500 °C and 5 kbar. Show all work. Section 3.5.3 (2nd. ed) of your textbook should be useful. c. Write and integrate the expression for the continuous change of molar ∆rH° as a function of CP. Then, manually calculate the molar ∆rH° in kJ/mol for albite Þ jadeite + quartz at 500 °C and 5 kbar. Show all work. Is this reaction exothermic or endothermic at this P and T?

Answer 1

The reaction for the problem is
NaAlSi₂O₆ + SiO₂ NaAlSi₃O₈
jadeite quartz high albite  

The P-T line can be described by the equation
P: 0.35+ 0.0265T (⁰C) 0.50k bar

The best values from phase equilibria
for the 298 K, I bar, thermochemical data for synthetic high albite are
=  -3922170 + 4300 J mol^-1

^{Therefore as we know,} ∆rH° = m C_p dT

Thus C_p= = -19395.39604  J mol^-1 K^-1

At any given temperature, C_p =

Thus, = -3917870 J mol^-1  

^{Since enthalpy is negative, that means system is gaining heat, so, the reaction is endothermic.}