While ethanol (CH3CH2OH) is produced naturally by fermentation, e.g. in beer- and wine-making, industrially it is synthesized by reacting ethylene (CH2CH2) with water vapor at elevated temperatures. A chemical engineer studying this reaction fills a 100. L tank at 21. °C with 34. mol of ethylene gas and 15. mol of water vapor. He then raises the temperature considerably, and when the mixture has come to equilibrium determines that it contains 24. mol of ethylene gas and 5.0 mol of water vapor. The engineer then adds another 11. mol of ethylene, and allows the mixture to come to equilibrium again. Calculate the moles of ethanol after equilibrium is reached the second time. Round your answer to 2 significant digits.

Respuesta :

Answer: The number of moles of ethanol after equilibrium is reached the second time is 11. moles.

Explanation:

We are given:

Initial moles of ethene = 34 moles

Initial moles of water vapor = 15 moles

The chemical equation for the formation of ethanol follows:

              [tex]CH_2=CH_2+H_2O\rightleftharpoons CH_3CH_2OH[/tex]

Initial:            34          15

At eqllm:     34-x           15-x            x

We are given:

Equilibrium moles of ethene = 24 moles

Equilibrium moles of water vapor = 5 moles

Calculating for 'x'. we get:

[tex]34-x=24\\\\x=10[/tex]

Volume of container = 100.0 L

The expression of [tex]K_c[/tex] for above equation follows:

[tex]K_c=\frac{[CH_3CH_2OH]}{[CH_2=CH_2][H_2O]}[/tex]      .......(1)

[tex][CH_3CH_2OH]=\frac{10}{100}=0.1M[/tex]

[tex][CH_2=CH_2]=\frac{24}{100}=0.24M[/tex]

[tex][H_2O]=\frac{5}{100}=0.05M[/tex]

Putting values in expression 1, we get:

[tex]K_c=\frac{0.1}{0.24\times 0.05}\\\\K_c=8.3[/tex]

Now, 11 moles of ethene gas is again added and equilibrium is re-established, we get:

The chemical equation for the formation of ethanol follows:

              [tex]CH_2=CH_2+H_2O\rightleftharpoons CH_3CH_2OH[/tex]

Initial:         24+11          5              10

At eqllm:     35-x          5-x            10+x

[tex][CH_3CH_2OH]=\frac{10+x}{100}[/tex]

[tex][CH_2=CH_2]=\frac{35-x}{100}[/tex]

[tex][H_2O]=\frac{5-x}{100}[/tex]

Putting values of in expression 1, we get:

[tex]8.3=\frac{\frac{(10+x)}{100}}{\frac{(35-x)}{100}\times \frac{(5-x)}{100}}\\\\8.3=\frac{(10+x)\times 100}{(35-x)\times (5-x)}\\\\x^2-52x+55=0\\\\x=50.9,1.1[/tex]

The value of 'x' cannot exceed '35', so the numerical value of x = 50.9 is neglected.

Moles of ethanol = [tex](10+x)=10+1.1=11.[/tex]

Hence, the number of moles of ethanol after equilibrium is reached the second time is 11. moles.

The number of moles of ethanol reached is : 11 moles

Given data :

moles of ethene ( initial ) = 34

moles of water vapor ( initial ) = 15

Volume of container = 100 L

Expressing the Chemical equation for the formation of ethanol

                         CH₂ + H₂O ⇄ CH₃CH₂OH  ----- ( 1 )

at Equilibrium : 34-x   15-x          x

Given that :

Equilibrium moles of ethene = 24

Eq moles of water vapor = 5

solve for x

x = 10

Following the expression of Kc for  equation 1

The concentration of [ H₂O ] = 5 / 10 = 0.05 M

Kc = [tex]\frac{0.1 }{0.24 * 0.05}[/tex]  = 8.3

Given that 11 moles of ethene is added again and equilibrium is reestablished

                        CH₂ + H₂O ⇄ CH₃CH₂OH

At equilibrium : 35-x   5-x        10+x

[ H₂O ] = ( 5-x ) / 100

solve for x using the expression for Kc

x = 50.9 , 1.1

we neglect the value of 50.9

therefore x = 1.1

moles of ethanol = 10 + 1.1 = 11

Hence we can conclude that  the number of moles of ethanol after equilibrium is reached the second time is 10 + 1.1 = 11

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