Select all of the following equations that represent an exothermic reaction.

NH3 (g) + 12.0 kcal → ½N2 (g) + 3/2 H2 (g)

C (graphite) → C (diamond), ΔH = - 0.45 kcal

C + 2S → CS2, ΔH = 27,550 cal

CH4 + 2O2 → CO2 + 2H2O + 212,800 cal

2H2O → 2H2 + O2, ΔH = + 58 kcal

Exothermic reactions:

1) release heat to the surroundings

2) the change of enthalpy, ΔH, is negative: ΔH < 0

3) the temperature of the system increases

With that you can conclude about every equation given:

NH3 (g) + 12.0 kcal → ½N2 (g) + 3/2 H2 (g) : is not exothermic because heat in the side of the reactants means that heat is being used, not released.

C (graphite) → C (diamond), ΔH = - 0.45 kcal : is exothermic because ΔH is negative

C + 2S → CS2, ΔH = 27,550 cal: is not exothermic because ΔH is positive

CH4 + 2O2 → CO2 + 2H2O + 212,800 cal : is exothermic because heat appears as a product of the reaction, which means that it is released.

2H2O → 2H2 + O2, ΔH = + 58 kcal : is not exothermic because ΔH is positive.