Alternative transcript:

added to a copper can. •the spirit burner containing the alcohol is weighed to 2d.p on a balance. • initial temperature of water is recorded. alcohol ignited and water Stirred continuously. •once temperature has risen by about 20°C then flame extinguished and spirit burner is re-weighed. • final temperature of water is recorded. SOURCES OF ERROR • heat lost to surroundings and calorimeter to minimise heat loss, copper cup must be close to the flame and a lid placed over it. •Shielding can reduce draughts. • Incomplete combustion. HEAT ENERGY CHANGE MASS OF WATER (9) = mcAT TEMPERATURE CHANGE HEAT ENERGY SPECIFIC HAT CAPACITY ENERGY REACTANTS AH ACTIVATION ENERGY REACTION PROFILES Snows the amount of energy that a substance has at the start and end of the reaction. EXOTHERMIC-lose energy as they form products →ENDOTHERMIC - reactants have less energy than products. PRODUCTS EXOTHERMIC ENTHALPY CHANGE (AH) IS NEGATIVE MOLAR ENTHALPY CHANGE KJ MOL™¹ ENTHALPY CHANGE (J/mol) 0=0 O=O BOND BREAKING- ENDOTHERMIC PROCESS BOND MAKING - EXOTHERMIC PROCESS CH 4 +20₂ ENERGY AH = Q moles HEAT ENERGY (KJ) -CO₂ ACTIVATION ENERGY REACTANTS BOND ENERGIES bond energies can also be used to calculate enthalpy change different bands require different amounts of energy to be broken. ENTHALPY CHANGE (AH) - ENERGY TO BREAK BONDS-ENERGY RELEASED MAKING BONDS NOTE: You will be given average band energies but you may have to work out how many there are of each bond. EXAMPLE FOR METHANE BURNING IN OXYGEN make sure to conver by +1000 JKJ PRODUCTS AH ENDOTHERMIC ENTHALPY CHANGE (AH) IS POSITIVE H-OH H-O-H + 2 H₂O -> O=C=0+