Determine the mole fraction of trans-2-hexene in the vapor phase (at -25 °C)?

[匿名]

2016-06-14 3:03 am

Use the vapour pressures (at -25 °C) of the pure substances below to answer the following questions.

Substance P* (kPa)
trans-2-hexene (C6H12) 1.37
ethyl formate (C3H6O2) 2.06

1. Determine the partial pressure (in kPa) of ethyl formate (C3H6O2) in the vapour phase (at -25 °C) over a solution for which the mole fraction of trans-2-hexene (C6H12) is 0.529. Report your answer to three significant figures in scientific notation. ANS: 9.69×10-1 kPa

2. A solution of trans-2-hexene (C6H12) and ethyl formate (C3H6O2) is prepared by adding 8.7 g of trans-2-hexene to 5.93 g of ethyl formate. Determine the mole fraction of trans-2-hexene in the vapor phase (at -25 °C). Report your answer to three significant figures in scientific notation.

回答 (1)

fooks

2016-06-14 4:50 am

✔ 最佳答案

vapour pressure of C₆H₁₂, P°(C₆H₁₂) = 1.37 kPa
vapour pressure of C₃H₆O₂, P°(C₃H₆O₂) = 2.06 kPa

(1)
In the solution :
Mole fraction of C₆H₁₂, X(C₆H₁₂) = 0.529
Mole fraction of C₃H₆O₂, X(C₃H₆O₂) = 1 - 0.529 = 0.471

By Raoult's law, the partial pressure of C₃H₆O₂, P(C₃H₆O₂)
= X(C₃H₆O₂) × P°(C₃H₆O₂)
= 0.471 × 2.06 kPa
= 0.970 kPa

(2)
Molar mass of C₆H₁₂ = (12.01×6 + 1.008×12) g/mol = 84.16 g/mol
Molar mass of C₃H₆O₂ = (12.01×3 + 1.008×6 + 16.00×2) g/mol = 74.08 g/mol

In the solution :
Mole fraction of C₆H₁₂, X(C₆H₁₂) = (8.7/84.16) / [(8.7/84.16) + (5.93/74.08)] = 0.564
Mole fraction of C₃H₆O₂, X(C₃H₆O₂) = 1 - 0.564 = 0.436

In the vapour phase :
Partial pressure of C₆H₁₂, P(C₆H₁₂) = X(C₆H₁₂) × P°(C₆H₁₂) = 0.564 × 1.37 kPa = 0.773
Partial pressure of C₃H₆O₂, P(C₃H₆O₂) = X(C₃H₆O₂) × P°(C₃H₆O₂) = 0.436 × 2.06 kPa = 0.898 kPa
Mole fraction of C₆H₁₂, X'(C₆H₁₂) = 0.773 / (0.773 + 0.898) = 0.463

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