If the given thermochemical equation is multiplied by 3 then,
ΔrH0 = 3ΔH0 = 3 × (-323) = -969 kJ
(b) If the direction of equation is reversed, then the reaction will be,
O2(g) + 2HF(g) → OF2(g) + H2O(g)
∴ ΔrH0 = – ΔH0 
= – (- 323) 
= + 323 kJ

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