>Combustion of Methane:

```

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

```

Enthalpy change: ΔH = -890 kJ/mol

This reaction is exothermic because it releases heat to the surroundings.

---

2.

>Decomposition of Water:

```

2H₂O(l) → 2H₂(g) + O₂(g)

```

Enthalpy change: ΔH = +286 kJ/mol

This reaction is endothermic because it absorbs heat from the surroundings.