Chemical Energetics simplified

Energy Changes energy profile diagram: energy against progress of reaction not time!! if the question asks for calculation on energy absorbed/released: dont make it + or - calculating energy change - enthalpy change: energy absorbed for bond breaking (+) + energy released for bond breaking (-) no need memorise, is given if needed Bond Energy (kJ/mol) Bond Energy (kJ/mol) Bond Energy (kJ/mol) Bond Energy (kJ/mol) H - H 436 I - I 151 C - C 350 C = O 740 O = O 496 H - F 562 C = C 610 N - H 390 N ≡ N 994 H - Cl 431 C ≡ C 840 N - N 160 F - F 158 H - Br 366 C - H 410 N = N 410 Cl - Cl 244 H - I 299 C - Cl 340 O - H 460 Br - Br 193 C - O 360 O - O 150 1. write balanced chemical equation 2. draw the bonding for each part of element 3. add up positive energy for bond breaking 4. add up negative energy for bond forming - tada!! energy change for whole reaction is in kJ/mol, must have + or - - UNLESS u have the kJ/mol but they ask you to tweak it for some specific number of mol, then just use kJ

TLDR Exothermic Endothermic Definition energy released = negative change temperature of surroundings increase energy absorbed = positive change temperature of surroundings decrease How yk? Total energy absorbed to break the bonds in A moles of HZ and B moles of XY is less than the total energy released to form bonds in C moles of ZY. Hence energy is released to surroundings Total energy absorbed to break the bonds in A moles of HZ and B moles of XY is morethan the total energy released to form bonds in C moles of ZY. Hence energy is absorbed from surroundings Energy profile diagram Energy level diagram (NO CURVE)

Chemical processes (WHEN IN DOUBT …CALCULATE IT OUT??) think about is there any energy being used? need fire for reaction? Chemical energy -> heat 1. Combustion (substance reacts w O2 to form CO2 and H2O) 2. Respiration (opposite of photosynthesis) 3. Neutralisation (acid/base + smt = water + salt) 4. Displacement of metals 5. Acid + metal 6. Adding water to concentrated H2SO4 7. Group 1 + water 8. Reducing iron (III) oxide with CO (extract iron) 9. Haber process (producing ammonia) 10. Adding water to anhydrous substances Chemical energy -> electrical energy 1. Electric/Simple cell 2. Fuel cell Chemical energy -> Nuclear energy 1. Fission of Uranium atoms (splits into 2) Heat -> Chemical energy 1. Addition of water to substances like NH4Cl. Ca(NO3)2, KNO3 2. Thermal decomposition of metal carbonates Light energy -> Chemical energy 1. Photosynthesis (CO2 + H2O = C6H12O6 + O2) 2. Photochemical reaction Electrical energy -> Chemical energy 1. Electrolysis of molten lead (II) bromide, aqueous sulfuric acid, aqueous sodium chloride, aqueous copper (II) sulfate (opposite of simple cells) Physical processes Condensation, Freezing - Heat released to strengthen attractive forces between particles (rmb forming bonds is - chang