Equilibrium in Chemical Reactions

Steps:

• Identify the reaction as reversible, indicated by the double arrow ⇌.
• Recall that equilibrium occurs when rates of forward and reverse reactions balance.
• Evaluate each option against the definition of dynamic equilibrium.
• Select the option matching the equal rates condition.

Why B is correct:

• By definition, chemical equilibrium means forward and reverse reaction rates are equal, so concentrations remain constant.

Why the others are wrong:

• A: At equilibrium, concentrations do not change with time.
• C: ΔH = +170 kJ/mol shows the forward reaction is endothermic and absorbs heat.
• D: Both sides have 2 molecules (1 N₂ + 1 O₂ = 2; 2 NO = 2).

Final answer: B