Objective: Whenever chemical reactions occur, energy is transferred to or from the surroundings. An exothermic reaction is one which transfers heat energy to the surroundings An endothermic reaction is one which takes heat energy from the surroundings

ReactionStarting temp. (ºC) Final temp. (ºC) Exothermic or endothermic A + B1927 C + D2025 E + F Decide whether each of the above reactions is exothermic or endothermic? 2. If the volume of solution was the same in each reaction. Which had the largest energy change?

ReactionEnergy change +ve: energy given out -ve: energy taken in Exothermic or endothermic Methane + Oxygen 890 Ammonium chloride + water -15 Glucose + Oxygen 2802 Ammonium chloride  Ammonia + Hydrogen chloride -176 Nitrogen + Hydrogen 92

Objective: In a reversible chemical reactions, the products of the reaction can react to produce the original reactants. A reversible reaction is denoted by the double arrows A + B C + D A & B are reactantsC & D are products If a reversible reaction is exothermic in one direction. It is endothermic in the other direction.

Adding water to anhydrous copper sulphate is exothermic. Anhydrous copper sulphate is white. Anhydrous is pronounced "an-high-drus“ Anhydrous means "without water". Anhydrous copper sulphate is copper sulphate which is completely dry. When water is added to it, it turns into the familiar hydrated blue crystals. Hydrated copper sulphate anhydrous copper sulphate + water Hydrated is pronounced "high-dray-tid", it means 'with water'. If blue (hydrated) copper sulphate are heated, an endothermic reaction occurs, they lose their water, turn white and become anhydrous copper sulphate. This reaction is reversible.

Work in groups of four and carry out the following experiment: 1. Place about 4 spatulas of hydrated copper sulphate in a crushable 2. Heat the copper sulphate using a hot plate until it changes color. 3. Leave it to cool down for 5 minutes. 4. Place the crucible student should hold the bottom of the tube carefully while the partner adds water drop by drop from a pipette. Answer the following questions in your books (in full sentences): What colour was the copper sulphate at the start? What colour was the copper sulphate at the end? What did you observe at the top of the tube? What colour did the copper sulphate change to after adding the water? What does blue copper sulphate have that white copper sulphate doesn’t? What did you feel at the bottom of the tube after adding the water? Which reaction was exothermic? Which reaction was endothermic?