chapter 9 - enthalpy Flashcards
chemical energy
the energy stored in the bonds of atoms
enthalpy
the heat content that is stored in a chemical system
exothermic reactions
ΔH = -ve products have less chemical energy than reactants heat given to surroundings
endothermic reactions
ΔH = +ve products have more chemical energy than reactants heat gain from surroundings
activation energy
minimum energy required to break the bonds in the reactants for the reactions to happen
average bond enthalpy
the energy required to break one mole of a specific type of bond in a gaseous molecule
calculating energy changes
ΔH = Σ(bond enthalpies of bonds broken) - Σ(bond enthalpies of bonds made)
standard conditions
- 298K - 100kPa - 1.00 mol dm-1
standard enthalpy change of reaction ΔrH∘
the enthalpy change that occurs when molar quantities stated in a chemical equation react under standard conditions
standard enthalpy change of combustion ΔcH∘
enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions
standard enthalpy change of neutralisation ΔneutH∘
enthalpy change that takes place when an acid and base react to form one mole of H2O under standard conditions
standard enthalpy change of formation ΔfH∘
enthalpy change that takes place when one mole of a compound is formed from its consitituent elements in standard conditions
determination of energy change calculation
Q = MCΔT
hess’ law
states that if a reaction can take place by more than one route, as long as the conditions are the same at the start as they are at the end, then the overall enthalpy change should be the same
calculation from using formation data for constructing Hess cycles
ΔHr = ΣΔH products - ΣΔH reactants
calculation from using combustion data for constructing Hess cycles
ΔHr = ΣΔH reactants - ΣΔH products
