# Three thermochemical equations are given below(i) $C_{\left ( graphite \right )}+O_{2}\left ( g \right )\rightarrow CO_{2}\left ( g \right );$                                                             $\Delta _{r} H^{o}=xkJmol^{-1}$(ii) $C_{\left ( graphite \right )}+\frac{1}{2}O_{2}\left ( g \right )\rightarrow CO\left ( g \right );$                                                               $\Delta _{r} H^{o}=ykJmol^{-1}$(iii) $CO\left ( g \right )\frac{1}{2}O_{2}\left ( g \right )\rightarrow CO_{2}\left ( g \right );$                                                          $\Delta _{r} H^{o}=zkJmol^{-1}$Based on the above equations, find out which of the relationship given below is correct? Option 1) x=y-z Option 2) z=x+y Option 3) x=y+z Option 4) y=2z-x

As we learnt in

Hess's Law -

The total amount of heat change in a chemical reaction is the same whether the reaction is carried  out in one or several steps by one or more methods.

- wherein

$C_{(s)}+O_{2(g)}\rightarrow CO_{2(g)}$

$\Delta H= 393.5\, kj$

$C_{(s)}+\frac{1}{2}O_{2(g)}\rightarrow CO_{(g)}$

$\Delta H_{1}= 110.5\, kj$

$CO_{(g)}+\frac{1}{2}O_{2(g)}\rightarrow CO_{2(g)}$

$\Delta H_{2}= 283.0\, kj$

$\Delta H= \Delta H_{1}+\Delta H_{2}$

According to Hest law, equation

(i) is sum of equation (ii) and (iii)

Option 1)

x=y-z

This option is incorrect

Option 2)

z=x+y

This option is incorrect

Option 3)

x=y+z

This option is correct

Option 4)

y=2z-x

This option is incorrect

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