Stoichiometry + Energetics

what is meant by the system?

the chemicals that react

why is heat loss a source of error in calorimetry?

heat escapes from the calorimeter and the temperature change is less than the actual one

why is incomplete combustion a source of error in calorimetry?

fuel may not burn completely and less heat is released than expected

why is specific heat capacity assumption an error in calorimetry?

for the solution it is assumed that its specific heat capacity is the same as of pure water

what is average bond enthalpy

mean energy to break a bond in a gas phase averaged over many compounds

what is meant by the standard enthalpy of combustion?

enthalpy change when 1 mol of a substance burns completely in excess oxygen under standard conditions

what is meant by the standard enthalpy of formation

enthalpy change when 1 mol of a compound forms from its elements under their standard states

why are combustion reactions usually exothermic?

bonds in products are stronger than those in reactants, more energy is released in forming product bonds than in breaking reactant bonds

What is Hess’s law?

the total enthalpy change of a reaction is independant of the pathway taken, provided the reactant and products remain the same

what does complete combustion produce?

carbon dioxide and water

what does incomplete combustion produce

carbon monoxide water and soot

what does a lower energy (shown by enthalpy change) indicate?

more stable