A 5.00 mol sample of carbon dioxide undergoes a two-step process. First, at a co

Question

A 5.00 mol sample of carbon dioxide undergoes a two-step process. First, at a constant volume, the gas behaves ideally as it is cooled from 47.0 degrees Celcius to -78.5 degrees Celcius where it reaches a pressure of 1 atm. Second, at -78.5 degrees Celcius and a constant pressure of 1 atm, the gas undergoes a phase change to dry ice. What is the change in internal energy of carbon dioxide for this entire process?

The constant volume molar heat capacity of carbon dioxide gas C_V is 28.46 J/mol . K, the heat of sublimation L_s of carbon dioxide is 6030 cal/mol, and the density of dry ice is 3.41 * 10^4 mol / m^3.

Part C

What is the change in internal energy delta U of carbon dioxide for this entire process?

Express your answer in joules

Explanation / Answer

delta U1 = n Cv ln T2/T1

=5 * 28.46 * (194.5-320) = -17858.65 J =- 17.858 KJ = - 17.858/4.18 KCal =- 4.271 KCal

delta U2 = delta Q = 6030*5 = 30.15 Kcal

Total change in internal energy = 30.15 - 4.271 = 25.879 KCal

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