Energetics Flashcards
bonds broken
energy taken in
bonds made
energy given out
if overall energy is taken in
energy change is positive
overall energy is released
energy change is negative
enthalpy change
ΔH
heat energy change measured under conditions of constant pressure
kJmol-1
standard enthalpy of combustion
enthalpy change when 1 mol of a compound is completely burned in oxygen under standard conditions
standard enthalpy of formation
enthalpy change when 1 mol of a compound is formed from its elements in their standard states under standard conditions
specific heat capacity
q = m c Δt
q = heat change
m = mass
c = shc
t = temp change
define shc
energy required to raise 1 kg if a substance by 1K without a change of state
ΔH formula
q / mol
Hess’ Law
enthalpy of a reaction is independent of the route taken as long as the initial and final conditions are the same
used to measure enthalpy change of a reaction that cannot be measured experimentally
why is the overall enthalpy change for a reaction the same regardless of route taken
energy in a reaction system must be conserved- can’t be created or destroyed
mean bond enthalpy
enthalpy needed to break covalent bonds into gaseous atoms averaged over different molecules
slightly less accurate than Hess’s Law
breaking bonds
endothermic , so bond enthalpies are always positive
∆H
∆H = ∑∆H(Bonds broken) - ∑∆H(Bonds Formed)
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