Question

Calculate the standard enthalpy change for the phase transition reaction of solid carbon dioxide (dry ice) at -78.5°C to gaseous carbon dioxide at 1 atm and 25°C given that the enthalpy of formation of solid carbon dioxide and gaseous carbon dioxide are -393.5 kJ/mol and -393.5 kJ/mol, respectively.

Answer 1

To calculate the standard enthalpy change for the phase transition reaction of solid carbon dioxide  dry ice  at -78.5C to gaseous carbon dioxide at 1 atm and 25C, we need to consider the following steps:1. Heating solid CO2 from -78.5C to 0C2. Sublimation of solid CO2 at 0C to gaseous CO23. Heating gaseous CO2 from 0C to 25CStep 1: Heating solid CO2 from -78.5C to 0Cq1 = m * C_s * Twhere m is the number of moles, C_s is the specific heat capacity of solid CO2, and T is the change in temperature.The specific heat capacity of solid CO2 is approximately 0.835 J/gK. Assuming 1 mole of CO2, the molar mass of CO2 is 44.01 g/mol.q1 =  44.01 g/mol  *  0.835 J/gK  *  0 -  -78.5C  q1 = 2883.6 J/molStep 2: Sublimation of solid CO2 at 0C to gaseous CO2The enthalpy of sublimation for CO2 is 25.2 kJ/mol.q2 = 25.2 kJ/mol * 1000 J/kJq2 = 25200 J/molStep 3: Heating gaseous CO2 from 0C to 25Cq3 = m * C_g * Twhere C_g is the specific heat capacity of gaseous CO2.The specific heat capacity of gaseous CO2 is approximately 0.854 J/gK.q3 =  44.01 g/mol  *  0.854 J/gK  *  25C - 0C q3 = 940.7 J/molNow, we can calculate the total enthalpy change for the phase transition:H_total = q1 + q2 + q3H_total = 2883.6 J/mol + 25200 J/mol + 940.7 J/molH_total = 29024.3 J/molTherefore, the standard enthalpy change for the phase transition reaction of solid carbon dioxide  dry ice  at -78.5C to gaseous carbon dioxide at 1 atm and 25C is approximately 29.0 kJ/mol.