Physical chemistry Flashcards
define enthalpy change
the heat energy transferred in a reaction at standard conditions (constant pressure)
what is the standard pressure condition ?
100kPa (about 1 atm)
what is the standard temp condition ?
298K
name an exothermic reaction
combustion
name an endothermic reaction
thermal decomposition
what is the symbol for activation energy ?
Ea
what is standard enthalpy change of reaction ?
E.C. when reaction occurs in molar quantities shown in the chemical equation, under S.C.
what is standard enthalpy change of formation ?
E.C. when 1 mole of a compound is formed from its elements in their standard states, under S.C.
what is standard enthalpy change of combustion ?
E.C. when one mole of a substance is completely burned in oxygen, under S.C.
what is standard enthalpy change of neutralisation ?
E.C. when an acid and an alkali react together, under S.C., to form 1 mole of water
to break bonds, energy is …
needed
to make bonds, energy is …
released
describe the bonds in endothermic
bonds are broken
describe the bonds in exothermic
bonds are formed
what is bond dissociation enthalpy ?
amount of energy needed to break bonds per mole
what to remember with enthalpy change reactions
the sign (+ or -)
what is Hess’s law ?
total enthalpy change is always the same, no matter which route is taken
what is the standard change of formation of any element ?
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