A) \[-\,160\text{ }kJ/mol\]
B) \[-\,72\text{ }kJ/mol\]
C) \[{{H}_{2}}{{O}_{2}}\]
D) \[-\,36\text{ }kJ/mol\]
Correct Answer: B
Solution :
In polymerization of ethane\[n\,({{H}_{2}}C=C{{H}_{2}})\xrightarrow{Polymerisation}{{(-\,C{{H}_{2}}-C{{H}_{2}}-)}_{n}}\] |
Since, the no. of \[C-H\] bonds on both sides are equal. But n(C=C) changes to \[2n\,\left( C-C \right)\] bonds + 1. |
or a C = C double bond changes to 3 \[\left( C-C \right)\]single bond |
one bond each by \[C{{H}_{2}}\] group \[C-C\] and one bond extra. |
\[n\,(C=C)=2n\,(C-C)+1\] |
Since n is very large as compared to |
\[n\,(C=C)\to 2n\,(C-C)\] |
Enthalpy of polymerization |
\[=n\,\,(\Delta \,{{H}_{c=c}})-2n\Delta {{H}_{c\,-\,c}}\] |
\[=n\,\,\times \,\,590-2n\,\,\times \,\,331=-\,72n\] |
Enthalpy of polymerization per molecule |
\[=\frac{\Delta \,{{H}_{polymerisation/mol}}}{n}=-\frac{72n}{n}=-\,72\,kJ/mol\] |
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