The document discusses chemical energetics, emphasizing the energy changes during reactions, distinguishing between exothermic and endothermic processes. It explains how to calculate enthalpy changes (∆h) and provides examples of reactions, showcasing the principles of energy absorption and release associated with bond breaking and formation. The conservation of energy in chemical reactions is highlighted, along with the significance of bond energies.

1. Chemical Energetic(Energy of Reaction)

2. Why do we need to study chemical energetics?It can lead us to understand a chemical change better. E.g What is the temperature for a reaction to occur.It will also tell us the energy barrier that reactants have to overcome before becoming products.

3. Energetics of chemical reactionsEvery reactant will have a discrete amount of energy.rearrangement of atoms that occurs in a chemical reaction is virtually always accompanied by the liberation or absorption of heat.Bonds are broken in reactants and bonds are formed in product

4. System and surroundingsWe will use 2 models to represent reactants and its environments around it.System – ReactantsSurroundings – Environment around reactants

5. Exothermic ReactionHeat is given offAs a result of this release of heat energy from the system (reactants), the surrounding will have a increase in temperatureEnergy of reactant < Energy of Surrounding

6. Exothermic ReactionSo what happens after heat energy is being released?Products formed will have a energy level lower than reactants.Conservation of energy!

7. Exothermic ReactionExample of Exothermic ReactionCarbon combust under presence of oxygen to produce carbon dioxide.Neutralisation between an acid and alkali3. Granular Zinc with Tin(II)Chloride. (Metal displacement)

8. Endothermic Reactionheat energy is taken in. System (reactants) take in energy from the surrounding.Surrounding loses heat to the reactants.Energy of reactant > Energy of Surrounding

9. Endothermic ReactionSo what happen after heat energy is being absorbed? Product formed will have a higher energy than the reactants.Conservation of energy!

10. Endothermic ReactionExamplesThermal decompositionHydrated copper (II) sulfate ----> Anhydrous Copper (II) sulfateCaCO3 --------> CaO + CO22) Photosynthesis3)

11. So what do we name the difference in amount of energy between reactants and products? ENTHALPY CHANGE OF REACTION∆HThe Enthalpy change in a reaction has a symbol ∆H.

12. EnthalpyEnthalpy (H) is also known as heat content, is the total energy of a system, some of which is stored as chemical potential energy inside the chemical bonding.Absolute enthalpies for particular states cannot be measured, but the change in enthalpy that occurs during a reaction can be measured – Using a calorimetry

13. Enthalpy∆H is positive (+) for endothermic reactions. Heat energy is gained by system from the surrounding. Hence the surrounding will a dip in temperature∆H is negative (-) for exothermic reactions. Heat energy is lost to the surrounding and cause the temperature in the surrounding to rise.

14. EnthalpyFor endothermic reaction, final products have a higher energy than the reactants.For Exothermic reaction, final products have a lower energy than the reactants.

15. Bond EnergyCovalent bonds exist in covalent compounds

16. These covalent bonds have a specific amount of energy to hold the atoms together

17. These energy is called BOND ENERGY

18. Energy is absorbed during bond breaking and energy is released during bond forming.How to calculate the enthalpy change of reaction?H2 + Cl2 -----> 2HCl ∆H = ? Step 1: Energy for some bonds will be given in the questionsStep2: Calculate the energy absorbed during bond breaking and energy is released during Bond forming

19. How to calculate the enthalpy change of reaction?Step 3: Energy is absorbed by the reactants when bonds are broken. Hence it will be 436KJ + 243KJ = 679KJEnergy is released by product when new bonds are formed.2 X 432KJ = 864KJStep4: ∆H = (Energy absorbed when bond are broken in reactants) – (Energy released when bonds are formed in product)

20. How to calculate the enthalpy change of reaction?Step 5: ∆H = (Energy absorbed when bond are broken in reactants) – (Energy released when bonds are formed in product)∆H = 679KJ – 864KJ = -185KJ

21. Assignment: Chemical EnergeticsQn 3a)2 H-O-O-H ------> O=O + 2 H-O-H ∆H= -206KJmol-1Thought process: Enthalpy change of reaction already shows that there is a decrease in value as shown in the negative sign. This implies that it is an exothermic reaction.This will also mean that energy from bond breaking(reactants) is less than bond formation (products)