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Question: Which of the following reactions is NOT exothermic?...

Which of the following reactions is NOT exothermic?

A

2KClO3(s)⟶2KCl(s)+3O2(g)+78 kJ2KClO_{3(s)} \longrightarrow 2KCl_{(s)} + 3O_{2(g)} + 78 \text{ kJ}

B

H2(g)+12O2(g)⟶H2O(l)+286 kJH_{2(g)} + \frac{1}{2}O_{2(g)} \longrightarrow H_2O_{(l)} + 286 \text{ kJ}

C

N2(g)+2O2(g)⟶2NO2(g)−66.4 kJN_{2(g)} + 2O_{2(g)} \longrightarrow 2NO_{2(g)} - 66.4 \text{ kJ}

D

CH4(g)+2O2(g)⟶CO2(g)+2H2O(l)+890 kJCH_{4(g)} + 2O_{2(g)} \longrightarrow CO_{2(g)} + 2H_2O_{(l)} + 890 \text{ kJ}

Answer

Option (C)

Explanation

Solution

For an exothermic reaction, energy is released (indicated by a positive value next to "kJ").

  • Reactions (A), (B), and (D) release energy (+78 kJ, +286 kJ, and +890 kJ, respectively).
  • Reaction (C) absorbs energy (-66.4 kJ), indicating an endothermic reaction.

Therefore, the reaction that is NOT exothermic is Option (C).