Energy Changes

• An exothermic reaction is one that transfers energy to the surrounding areas so the temperature of the surroundings increases.
• What are examples of exothermic reactions?

  Neutralisation, combustion, oxidation reactions.
• In exothermic reactions, the products have less energy than the reactants because energy has been transferred to the surroundings.
• An endothermic reaction is one that takes in energy from the surroundings so the temperature of the surroundings decreases.
• What are examples of endothermic reactions?

  Thermal decompositions (e.g. freezing) and the reaction of citric acid and sodium hydrogencarbonate.
• In endothermic reactions, the products have more energy than the reactants as they take in energy from their surroundings.
• The minimum amount of energy that particles must have to react is called the activation energy.
• In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds.
• In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.
• Why are instant cold packs shaken before use?

  So there are more collisions between the particles so the bag gets colder faster.
• What measurements could a student take to show a reaction is exothermic? How will this prove it is exothermic?

  Measure temperature at the start and measure temperature at the end. If reaction is exothermic, temperature will increase.
• In an exothermic reaction..

  energy released when bonds form is greater than energy used when bonds broken
• Explain why the temperature decreases then increases in the temperature changes practical.

  At first, the temperature decreases because the reaction is endothermic. The temperature then increases later on because energy transfers from the solution to the surroundings.
• Why does the mass change if there isn't a lid when conducting practicals.

  The mass decreases because products have escaped.
• Suggest why some particles do not react at room temperature?

  The particles collide but have insufficient energy at room temperature.
• Copper carbonate and sulfuric acid react to produce copper sulfate. What type of reaction is this?

  Exothermic or neutralisation
• In an endothermic reaction, the temperature of the solution will decrease.
• The temperature goes down after a reaction has stopped because the solution cools back to room temperature and the energy is lost to the surroundings