Module 13 Flashcards
Hess’s Law
Enthalpy is a state function and is therefore independent of path.
State function
any quantity that depends solely on the final destination, not on the way you get to that destination
for enthalpy, the amount of energy contained in a substance is
independent of how it is made
enthalpy of formation (ΔHf)
the ΔH of a formation reaction
standard conditions
a temp of 25 C and a pressure of 1.00 atm
standard enthalpies of formation
the ΔHf for molecules under standard conditions
denoted with an “°”
the ΔH° of any chemical reaction is the
sum of the ΔHf° for the products minus the sum of the ΔHf° for the reactants
when a reaction is exothermic energy will be thought of a s
a product in the reaction
when a reaction is endothermic energy will be thought of as
a reactant in the reaction
enthalpy
the energy stored in a substance
stated as the ‘enthalpy of that substance’
symbolized by ‘H’
change in enthalpy (ΔH)
the energy change that accompanies a chemical reaction
1 calorie =
4.184 Joules
ΔH is positive for – reactions and negative for – reactions
endothermic
exothermic
whether a reaction is exothermic or endothermic, energy is both– and– during the course of the reaction. the difference is —
absorbed
released
how much
bond energy
the strength of a chemical bond
ΔH=
energy required to bread bonds/ energy released when bonds form
the standard enthalpy of formation of an element in its elemental form is
zero
energy diagram
a ‘picture’ of the energy associated with a chemical reaction
reaction coordinate
tells us how close the reaction is to completion
plotted on the horizontal/ x axis of the graph
intermediate state/ activated complex
occurs at the top of the hump, which represents the midpoint of the reaction
activation energy
the energy necessary to start a chemical reaction
entropy
a measure of the disorder that exists in any system
denoted by an ‘S’
2nd law of thermodynamics
the entropy of the universe must always either increase or remain the same. It can never decrease
which state has the least amount of entropy associated with it? How about the middle amount? What about the highest amount?
solid
liquid
gaseous
the entropy of a system increases with – temp
increasing
the entropy of a system increases os the matter it contains–
increases
ΔS universe ≥
0
all substances, even elements have
an absolute entropy
what does the Gibbs Free equation tell us?
whether or not a reaction is consistent with the second Law of thermodynamics
if a reaction is consistent with the second law, we call it
spontaneous
this is because we know that it con proceed
if a reaction is ‘not spontaneous’ it means;
The reaction is not consistent with the second law and therefore cannot occur
when ΔG
is consistent with the second law
is spontaneous
when ΔG > 0 the reaction
is not consistent with the second law
cannot proceed
is not spontaneous
