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On the basis of thermochemical equations (a), (b) and (c), find out which of the algebraic relationships given in options (i) to (iv) is correct.

(a) C (graphite)+O_{2}(g)\rightarrow CO_{2}(g);\Delta _{r}H=x\; kJ\; mol^{-1}

(b) C (graphite)+\frac{1}{2}O_{2}(g)\rightarrow CO(g);\Delta _{r}H=y\; kJ\; mol^{-1}

(c) CO _{(g)} + \frac{1}{2}O_{2(g)}\rightarrow CO_{2(g)} ; \Delta _{r}H= z\; kJ\; mol^{-1}

(i) z = x + y
(ii) x = y – z
(iii) x = y + z
(iv) y = 2z – x

 

Answers (1)

The answer is option (iii) x = y + z  

x =y + z is the correct option as Algebraic sum of y and z will give x.

Explanation: When y is subtracted from x, we get z. Explained below:

C (graphite)+O_{2}(g)\rightarrow CO_{2}(g);\Delta _{r}H=x\; kJ\; mol^{-1}________(i)

C (graphite)+\frac{1}{2}O_{2}(g)\rightarrow CO(g);\Delta _{r}H=y\; kJ\; mol^{-1}________(ii)

When subtracted , we receive:

CO _{(g)} + \frac{1}{2}O_{2(g)}\rightarrow CO_{2(g)} ; \Delta _{r}H= z\; kJ\; mol^{-1}________(iii)

So, z= x-y, or, easily put, x=y+z. Hence, option c.

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