JEE MAIN - Chemistry (2019 - 12th January Evening Slot - No. 14)
Given
(i) C (graphite) + O2(g) $$ \to $$ CO2(g); $$\Delta $$rH$$^\Theta $$ = x kJ mol$$-$$1
(ii) C(graphite) + $${1 \over 2}$$O2(g) $$ \to $$ CO(g); $$\Delta $$rH$$^\Theta $$ = y kJ mol$$-$$1
(iii) CO(g) + $${1 \over 2}$$ O2(g) $$ \to $$ CO2(g); $$\Delta $$rH$$^\Theta $$ = z kJ mol$$-$$1
Based on the above thermochemical equations, find out which one of the following algebraic relationships is correct?
(i) C (graphite) + O2(g) $$ \to $$ CO2(g); $$\Delta $$rH$$^\Theta $$ = x kJ mol$$-$$1
(ii) C(graphite) + $${1 \over 2}$$O2(g) $$ \to $$ CO(g); $$\Delta $$rH$$^\Theta $$ = y kJ mol$$-$$1
(iii) CO(g) + $${1 \over 2}$$ O2(g) $$ \to $$ CO2(g); $$\Delta $$rH$$^\Theta $$ = z kJ mol$$-$$1
Based on the above thermochemical equations, find out which one of the following algebraic relationships is correct?
z = x + y
x = y + z
x = y – z
y = 2z – x
Explanation
In reaction (i), the product is CO2
If we add reaction (ii) and (iii) we get,
C + O2 $$ \to $$ CO2
here also product is CO2 from same reactant C and O2.
So according to hess law, we can say
x = y + z
If we add reaction (ii) and (iii) we get,
C + O2 $$ \to $$ CO2
here also product is CO2 from same reactant C and O2.
So according to hess law, we can say
x = y + z
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