Do Now: Calculate the mass of 4 mol of MgO Calculate the amount (in moles) or 32 g of NaCl Calculate the mass of 1.4 x 10-5 mol PbCl2 Calculate the mass of 2.46 x 10-3 mol CH4

Do Now: Copy and complete the table Solid Type of particle (atom, ion, molecule) Attractive forces Melting point (high or low) Aluminium Al Hydrogen sulfide H2S Graphite C Calcium oxide CaO

Solid Type of particle (atom, ion, molecule) Attractive forces Melting point (high or low) Aluminium Al Atom Metallic bond High Hydrogen sulfide H2S Molecule Weak intermoelcular forces low Graphite C Covalent bond high Calcium oxide CaO ion Ionic bond

Energy Changes

Kaupapa / Learning Outcome At the end of todays lesson I will be able to identify exothermic and endothermic reactions using energy diagrams, ΔrH values and heat changes.

Enthalpy Heat content of substance Symbol ➜ H Unit ➜ Kilojoules (Kj) Enthalpy change (ΔrH) = Hproducts - Hreactants

Exothermic Vs Endothermic video

Exothermic Reactants have more energy than products Releases energy Temperature of surroundings increases Feels warm Negative ΔrH or in products Forming bonds

Endothermic Reactants have less energy than products Absorbs energy Temperature of surroundings decreases Feels cold Positive ΔrH or in reactants Breaking bonds

Example The sublimation of carbon dioxide is overall an endothermic process CO2(s)  CO2(g) There are no weak intermolecular bonds between CO2 gas molecules. No bonds formed no energy out To break the weak intermolecular forces between CO2 molecules requires energy Overall: Since energy in > energy out = endothermic so ∆H is positive

If a reaction is endothermic in one direction it will be exothermic in the opposite directions A + B ➜ C + D (endothermic) C + D ➜ A + B (exothermic)

Complete pages 61-62