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Standard XII

Chemistry

Chemical Properties of Boron Family

24. Which sta...

Question

24. Which statements is/are incorrect ? (1) In alkali metals in a group, from top to bottom increase in size is maximum from Na to K (2) Addition of e in P atom will be exothermic (3) IP of F is greater than its EA value (4) Reaction O(g) + S(g) → O(g) + S(g) is endothermic

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The formation of the oxide ion requires first an exothermic and then an endothermic step as shown below

(a) $O_{g} + e^{-} = O_{g}^{-} △ H^{c i r c} = - 142 k j m o l^{- 1}$
(b) $O_{g} + e^{-} = O_{g}^{2 -} △ H^{c i r c} = 844 k j m o l^{- 1}$

This is because

Q. The formation of the oxide ion, O

_{(g)}^{2 -}

, from oxygen atom requires first an exothermic and then an endothermic step as shown below:

O_{(g)} + e^{-} \to O_{(g)}^{-}; Δ H^{\circ} = - 141 k J m o l^{- 1}

O_{(g)}^{-} + e^{-} \to O_{(g)}^{2 -}; Δ H^{\circ} = + 780 k J m o l^{- 1}

Thus, process of formation of

O^{2 -}

in gas phase is unfavourable even though

O^{2 -}

is isoelectronic with neon. It is due to the fact that:

Q. The formation of oxide ion,

O^{2 -} (g)

, from oxygen atom requires first an exothermic and then an endothermic step as shown below:

O (g) + e^{-} \to O_{(g)}^{-};_{Δ f} H^{⊖} = - 141 {kJ mol}^{- 1}

O^{-} (g) + e^{-} \to O_{(g)}^{2 -};_{Δ f} H^{⊖} = + 780 {kJ mol}^{- 1}

Thus the process of formation of

O^{2 -}

in gas phase is unfavourable even thought

O^{2 -}

is isoelectric with neon. It is due to the fact that,

Q. The formation of the oxide ion

O^{2 -} (g)

requires first an exothermic and then an endothermic step as shown below

O (g) + e^{-} \to O^{-} (g); △ H^{o} = - 142 k J m o l^{- 1}

O (g) + e^{-} \to O^{2 -} (g); △ H^{o} = - 844 k J m o l^{- 1}

The correct statement is:

Q. Consider the three statements about reaction energy diagrams and the relative magnitudes of the activation energy,

E_{a}

, and the enthalpy of reaction,

△ H

.
One or more of the statement is true.
Identify the correct statement or combination of statements from the four choices below.

	Statement
I	For an endothermic reaction, the magnitude of $E_{a}$ is always greater than $△ H$ .
II	For an exothermic reaction, the magnitude of $E_{a}$ is always greater than $△ H$ .
III	For an exothermic reaction, adding a catalyst will decrease the magnitude of $△ H$ .

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