which reaction is exothermic?\n○ $\\ce{ch_{4} + 2o_{2} -> co_{2} + 2h_{2}o + 891\\ kj}$\n○…

which reaction is exothermic?\n○ $\\ce{ch_{4} + 2o_{2} -> co_{2} + 2h_{2}o + 891\\ kj}$\n○ $\\ce{nh_{4}no_{3} + h_{2}o + 25\\ kj -> nh_{4}^{+}(aq) + no_{3}^{-}(aq)}$\n○ $\\ce{2h_{2}o + 286\\ kj -> 2h_{2} + o_{2}}$ \n○ $\\ce{n_{2} + o_{2} + 181\\ kj -> 2no}$

which reaction is exothermic?\n○ $\\ce{ch_{4} + 2o_{2} -> co_{2} + 2h_{2}o + 891\\ kj}$\n○ $\\ce{nh_{4}no_{3} + h_{2}o + 25\\ kj -> nh_{4}^{+}(aq) + no_{3}^{-}(aq)}$\n○ $\\ce{2h_{2}o + 286\\ kj -> 2h_{2} + o_{2}}$ \n○ $\\ce{n_{2} + o_{2} + 181\\ kj -> 2no}$

Answer

Explanation:

Step1: Recall exothermic definition

Exothermic reactions release energy (heat), so energy is a product (on right side of equation) or has positive energy released.

Step2: Analyze each option

  • Option 1: $\ce{CH_{4} + 2O_{2} -> CO_{2} + 2H_{2}O + 891\ kJ}$ – Energy (891 kJ) is a product, so heat is released (exothermic).
  • Option 2: $\ce{NH_{4}NO_{3} + H_{2}O + 25\ kJ -> NH_{4}^{+}(aq) + NO_{3}^{-}(aq)}$ – Energy is a reactant (absorbed), endothermic.
  • Option 3: $\ce{2H_{2}O + 286\ kJ -> 2H_{2} + O_{2}}$ – Energy is a reactant (absorbed), endothermic.
  • Option 4: $\ce{N_{2} + O_{2} + 181\ kJ -> 2NO}$ – Energy is a reactant (absorbed), endothermic.

Answer: $\ce{CH_{4} + 2O_{2} -> CO_{2} + 2H_{2}O + 891\ kJ}$ (the first reaction option)