RP2 Enthalpy Change

• use a polystyrene cup (not glass beaker) for insulation

• must record initial temp

• use a high enough concentration

• must measure temp. at intervals after addition and extrapolate to max. change → in order to calculate max. temp. change

Enthalpy of Combustion Values - why are they different?

• calorimetry values less exothermic → heat loss (copper absorbs some of the energy)

• calorimetry - incomplete combustion, some of the liquid can evaporate

• mean bond enthalpies over use values taken from a range of compounds

• bond enthalpy values ignore energy change in vaporisation of fuel or condensing water

Which value is it?

• experimental value will always be lower than true value due to heat loss/incomplete combustion

• experimental value MUST be less exothermic