Reversible Reactions & Equilibrium

Reversible reactions

• In a reversible reaction the products can react to re-form the reactants. It is written with the $\rightleftharpoons$ symbol: $\text{A} + \text{B} \rightleftharpoons \text{C} + \text{D}$
• The direction can be changed by changing the conditions
• Hydrated copper(II) sulfate is blue. Heating drives off the water to leave white anhydrous copper(II) sulfate; adding water turns it blue again and it gets hot:

$$\text{CuSO}_4 \cdot 5\text{H}_2\text{O} \rightleftharpoons \text{CuSO}_4 + 5\text{H}_2\text{O}$$

• Ammonium chloride splits into ammonia and hydrogen chloride when heated, and re-forms when cooled