of combustion of methane is –X kJ mol –1 . The value of is : (i) (ii) (iii) (iv) = 0 - Wired Faculty

Thermodynamics

Question

$increment straight U to the power of circled dash$ of combustion of methane is –X kJ mol^–1. The value of $increment straight H to the power of circled dash$ is :
(i) $equals increment straight U to the power of circled dash$
(ii) $greater than increment straight U to the power of circled dash$
(iii) $less than increment straight U to the power of circled dash$
(iv) = 0

Solution

The thermochemical equation for the combustion of methane is

CH subscript 4 left parenthesis straight g right parenthesis space plus space 2 straight O subscript 2 left parenthesis straight g right parenthesis space rightwards arrow space space space CO subscript 2 left parenthesis straight g right parenthesis space plus space 2 straight H subscript 2 straight O

Here comma space increment ng space equals space straight n subscript straight p space minus space straight n subscript straight r space equals space 1 minus 3 space equals space minus 2 semicolon We space know comma space space space space space space increment straight H to the power of circled dash space equals space increment straight U to the power of circled dash space plus space increment ngRT

Substituting the values, we have

increment straight H to the power of circled dash space equals space increment straight U to the power of circled dash space plus space increment ngRT space equals space minus straight X minus 2 RT

Here

increment straight H to the power of circled dash space less than space increment U to the power of circled dash

i.e. option (iii) is correct.

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