Exam 1 Flashcards
Endothermic
products are higher in energy than the reactants
increase in enthalpy
positive H
Exothermic
products are lower in energy than the reactants
decrease in enthalpy
negative H
When is there a negative H?
when the reaction is exothermic
When is there a positive H?
when the reaction in endothermic
bond enthalpy
change in enthalpy that is associated with breaking a particular bond in 1 mole of gaseous molecules
bond enthalpy in polyatomic molecules
hard to measure since it requires different amounts of energy to break the second bond versus the first
therefore, we use an average bond enthalpy for polyatomic molecules
What is enthalpy measured in?
kJ / mol
examples of intramolecular forces
covalent and ionic bonds
Entropy sign
S
Enthalpy sign
H
Entropy
a measure of how spread out or dispersed a systems energy is
Formula for the # of energetically favorable ways molecules can be arranged (W)
W = x^n
x= # of cells that can be occupied n= # of molecules
*relates to entropy
Protein folding and energy
decrease in entropy in the system because there are less possible arrangements
reaction is exothermic though so the surroundings experience an increase in entropy
this makes the universal entropy increase
entropy of a perfect crystalline
0 since molecules are set in place
allows us to determine the absolute entropy of crystalline solids
free energy
energy available to do work
G
gibb’s free energy
G < 0
spontaneous
G > 0
nonspontaneous
G = 0
at equilibrium
When does temperature come into play when determining spontaneity?
when both H (enthalpy) and S (entropy) are either both positive or both negative
in this case one must consider temperature
athermic
not producing or absorbing heat
What information do you use to calculate delta H?
bond energies
heat of a reaction
the difference in energy between the products and reactants
will the heat of a reaction be positive or negative for exothermic reactions? why?
negative since the products are lower in energy than the reactants