energetics Flashcards
what is an exothermic reaction?
where the overall energy is released to surroundings
–> + temperature
what is an endothermic reaction?
where the overall energy is entering the reaction from surroundings
–> - temperature
definition of enthalpy change
the change in heat content of a substance measured at constant pressure
what are the units of enthalpy?
KJ
what are the standard conditions for measuring enthalphy change?
298K - temperature
100kPa - pressure
what is standard enthalpy of combustion?
when 1 mol of a substance is burned completely in oxygen with all substances in standard states
what is always produced in a standard enthalpy of combustion equation?
H2O and CO2
what is standard enthalpy of formation?
when one mole of a substance is formed from its elements will all substances in standard states
equation for calulating enthalpy change (delta H)
q= m x c x (delta) T
(divide by 1000 and add -)
(delta) H= q/ mol
state Hess law
the enthalpy change is independent on route taken
define mean bond energies
the enthalpy change to break a covalent bond that is averaged to a range of compounds
what type of reaction is breaking bonds?
endothermic
(positive value)
what value would making bonds have?
negative values
