Q61 / 180 · NEET 2013 (Karnataka) · Chemistry

Three thermochemical equation are given below: (i) $\underset{\mathrm{kJJ} \mathrm{mol}^{-1}}{\mathrm{C}_{\text {(graphite) }}}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow \mathrm{CO}_{2(g)} \Delta \mathrm{H}^{\circ}=x$ (iii) $\mathrm{CO}_{(\mathrm{gJ})}+1 / 2 \mathrm{O}_{2(\mathrm{gk}} \rightarrow \mathrm{CO}_{2(\mathrm{~g}) i} \Delta \mathrm{H}^{\circ}=\mathrm{z}$ Based on the above equations, find out which of the relationship given below is correct.

  • A
    $z=x+y$
  • Correct answer
    B
    $x=y+z$
  • C
    $y=2 z-x$
  • D
    $x=y-z$

Solution

By considering the Hess's law equation (i) is equal to the sum of equation (ii) and (iii). Related Theory Hess's law states that heat absorbed or evolved in any chemical reaction is fixed quantity and is independent of the path of the reaction or the number of steps taken 0 obtain the reaction. $$ \Delta H_{n e t}=\Sigma \Delta H_r $$

Hence, the correct answer is option: 'B'.

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