Reactivity 1 (Energetics) Flashcards
standard enthalpy change of formation (ΔHf)
the enthalpy change that results when one mole of a compound is formed from its elements (in their standard states)
temperature
average kinetic energy of molecules
heat
amount of energy exchanged due to temperature difference between two substances (higher temp.<–> lower temp.)
enthalpy change
The change in internal (chemical) energy (H) in a reaction
(the enthalpy itself cannot be measured so we measure the change instead)
ΔH exothermic = (-)
ΔH endothermic = (+)
STABILITY
exothermic < endothermic
exothermic
((-)ΔH) heat energy transferred from system to surroundings ⁻⁻|_
- forming bonds
endothermic
((+)ΔH) system takes energy from surroundings _|⁻⁻
- breaking bonds
common experimental errors
- heat loss to the environment
- incoplete combustion
Assumptions
- no heat lost to the environment
- specific heat capacity is that of H2O
- Density is that of H2O
calculating ΔHrxn in terms of ΔHf
(ΔHf of products) - (ΔHf of reactants)
calculating ΔHrxn in terms of ΔHBE
(ΔHBE of reactants) - (ΔHBE of products)
[TABLE 12]
calculating ΔHrxn in terms of ΔHc
(ΔHc of reactants) - (ΔHc of products)
[TABLE 14]
Percentage Difference Formula
(Exp - Lit)/Lit *100
Entropy, S
- the distribution of available energy among the particles.
- measure of disorder of a system
(+) ΔS = more disorder
(-) ΔS = less disorder
ΔS
(ΔS of products) - (ΔS of reactants)
Spontaneity
A reaction which moves towards completion or equilibrium under a set of given conditions without external intervention
