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hram777 [196]
3 years ago
7

How to draw Hess' Cycle for this question ?

Chemistry
1 answer:
NISA [10]3 years ago
7 0

Answer : The standard enthalpy of formation of ethylene is, 51.8 kJ/mole

Explanation :

According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.

According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.

The formation reaction of C_2H_4 will be,

2C(s)+2H_2(g)\rightarrow C_2H_4(g)    \Delta H_{formation}=?

The intermediate balanced chemical reaction will be,

(1) C_2H_4(g)+3O_2(g)\rightarrow 2CO_2(g)+2H_2O(l)     \Delta H_1=-1411kJ/mole

(2) C(s)+O_2(g)\rightarrow CO_2(g)    \Delta H_2=-393.7kJ/mole

(3) H_2(g)+\frac{1}{2}O_2(g)\rightarrow H_2O(l)    \Delta H_3=-285.9kJ/mole

Now we will reverse the reaction 1, multiply reaction 2 and 3 by 2 then adding all the equations, we get :

(1) 2CO_2(g)+2H_2O(l)\rightarrow C_2H_4(g)+3O_2(g)     \Delta H_1=+1411kJ/mole

(2) 2C(s)+2O_2(g)\rightarrow 2CO_2(g)    \Delta H_2=2\times (-393.7kJ/mole)=-787.4kJ/mole

(3) 2H_2(g)+2O_2(g)\rightarrow 2H_2O(l)    \Delta H_3=2\times (-285.9kJ/mole)=-571.8kJ/mole

The expression for enthalpy of formation of C_2H_4 will be,

\Delta H_{formation}=\Delta H_1+\Delta H_2+\Delta H_3

\Delta H=(+1411kJ/mole)+(-787.4kJ/mole)+(-571.8kJ/mole)

\Delta H=51.8kJ/mole

Therefore, the standard enthalpy of formation of ethylene is, 51.8 kJ/mole

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Answer: 67.2 moles

Explanation: 2C_2H5+5O_2\rightarrow 4CO_2+2H_2O

According to the given balanced equation, 2 moles of acetylene C_2H_2 combine with 5 moles of oxygen O_2  to produce 4 moles of carbon dioxide CO_2.

Thus if 2 moles of acetylene C_2H_2 combine with = 5 moles of oxygen O_2

35 moles of acetylene C_2H_2 combine with=\frac{5}{2}\times {35}=87.5 moles of oxygen O_2

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5 moles of oxygen O_2 reacts with = 2 moles of acetylene C_2H_2

84 moles of oxygen O_2 reacts with=\frac{2}{5}\times {84}=33.6 moles of acetylene C_2H_2

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2 moles of acetylene C_2H_2  produce= 4 moles of carbon dioxide CO_2.

33.6 moles of acetylene C_2H_2 produce=\frac{4}{2}\times {33.6}=67.2 moles of of carbon dioxide CO_2.


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Answer: Option (d) is the correct answer.

Explanation:

It is given that molecular formula is C_{9}H_{16}. Now, we will calculate the degree of unsaturation as follows.

Degree of unsaturation = C_{n} - \frac{\text{monovalent}}{2} + \frac{\text{trivalent}}{2} + 1

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Yes, this compound could be an alkyne as for alkyne D.B.E = 2.

But this compound cannot be a cycloalkane because for a cycloalkane D.B.E = 1 which is due to the ring only.

Thus, we can conclude that it is a cycloalkane is not a structural possibility for this hydrocarbon.

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