Download Ch17-2 Driving Forces of Reactions

Thermal chemistry is study of the transfer of heat in
chemical reactions and physical changes.
• The student will be able to;
1. compare, contrast, analyze
Potential Energy diagrams
2. interpret numerical heat values
written in chemical reactions
Some reactions are:
exothermic = get hot = released heat
endothermic = get colder = absorbed heat
The energy of the chemical reaction
is displayed on a potential energy diagram.
Energy may be consumed or produced (exothermic or
endothermic) in a chemical reaction.
Enthalpy: change in energy
delta H j/mol
delta E j/mol
enthalpy
heat of reaction
Activation Energy: Ea
the energy needed to get the reaction started
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How is the height of the curve related to the
ease a reaction will occur?
What would the potential energy graph look
like for a rapid reaction?
What would happen if amount <Ea were
supplied?
Heat expressed in reactions.
l.
E- released H is negative,
E- absorbed H is positive.
2.
If H is + and written with products then exothermic
3C + Fe2O3
3CO + 2Fe + 110.53kj
3.
If H is + and written with reactants then endothermic
2H20(l) + 483.6 kj
2H2 (g) + O2 (g)
4.
If H is – and written with products then endothermic
3C + Fe2O3
3CO + 2Fe – 110.53kj
Reaction Rate: “How fast the reaction proceeds”
Reaction Rate depends on :
1. number of molecule collisions
2. efficiency of the collisions
5 factors can effect the rate of reaction:
l. Nature of reactants
2. surface area (big chunk vs. powder)
3. temperature ( hot or cold)
4. concentration
5. catalyst (only effects rate does not participate in
reaction…can recover.)
Thermal chemistry is study of the transfer of heat in
chemical reactions and physical changes.
• The student will be able to;
1. compare, contrast, analyze
Potential Energy diagrams
2. interpret numerical heat values
written in chemical reactions
Entropy
The student will :
have a conceptual understanding of
entropy and its application toward
reactions.
be able to determine the direction of
entropy when given a chemical reaction.
• Entropy: a measure of degree of randomness of the
molecules.
S
j/mol*K or kj/mol*K
Delta
“most reactions in nature are toward disorder”
Organized
disorganized
Entropy increases as phase change occurs from
solid to liquid to gas
S
Increase in entropy +
L
delta
g
S …..more crazy random (favored)
Decrease in entropy -
delta
S ……more organized
You can tell entropy by looking at the phases of the reaction
ws. 17.8
Entropy
The student will :
have a conceptual understanding of
entropy and its application toward
reactions.
be able to determine the direction of
entropy when given a chemical reaction.