Download Section 3B

2/7/14
Section 3B
Heat of Reaction
Energy
Energy: ability to do work or produce heat.
Types of energy
1) Potential energy - energy possessed by objects due
to position or arrangement of particles.
Forms of potential energy - electrical, chemical,
gravitational
2) Kinetic energy - energy of motion
3) Radiant energy - energy given off by subatomic
particles (such as photons, electrons, etc.) or
chemical reactions.
Law of Conservation of
Energy
Energy can not be created or destroyed, only
changed into some other type of energy.
Energy conversions can start or end up in
potential energy (chemical or position), kinetic
energy (mechanical) or radiant energy
(thermal, electrical, light, sound).
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Definition
Thermochemistry is the
study of the changes
in heat in a chemical
reaction.
Heat is measured in
Joules (J)
The heat of a reaction
depends on the
chemical energy of
the reactants in
comparison to the
chemical energy of
the products
Exothermic
An exothermic reaction is a
chemical reaction that
releases heat.
- “exo” means outside,
“thermes” means heat, so
this type of reaction
releases heat to the
outside of the reaction.
Endothermic
An endothermic reaction
is a chemical reaction
that absorbs heat.
- “endo” means inside,
“thermes” means heat,
so this type of reaction
takes heat inside the
reaction.
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Fuel Additives & Alternatives
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Group 1: Fuels (2)
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Group 2: Diesel (2)
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difference in composition,
proper use (which fuel to use),
knocking and pinging
types of emissions, dangers,
catalytic converter
Group 5: Clean Air Act (2)
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purpose, types of additives and their
effectiveness
Group 7: FlexFuel Engine Cars (4)
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Ethanol, E85, How they work,
Reasons for use, Advantages &
Disadvantages
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Group 8: Hybrid Engine Cars (4)
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Group 9: Electric Cars (4)
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Group 4: Vehicle Emissions (2)
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diesel, biodiesel, diesel engines
(how they work)
Group 6: Gasoline additives (2)
Group 3: Gasoline grades (2)
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octane, isooctane, kerosene,
cracking
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How they work, Why hybrid?,
Advantages & Disadvantages
How they work, Advantages &
Disadvantages
history, applications,
Environmental Protection
Agency
Enthalpy (Heat of Reaction)
Enthalpy is a measure of the heat (energy) absorbed
and released in a reaction. The symbol for enthalpy
is ΔH.
The enthalpy is either included in the equation:
2C2H6 + 7O2 --> 4CO2 + 6H2O + 3120 kJ
Or at the end of the reaction:
2C2H6 + 7O2 --> 4CO2 + 6H2O, ΔH = -3120 kJ
A negative enthalpy means the reaction is exothermic
because the reactants have lost energy. Heat has
been released.
What type of reaction would exist if the heat energy
were a reactant? If the enthalpy were positive?
27KJ + NH4NO3 --> NH4+ + NO3NH4NO3 --> NH4+ + NO3-, ΔH = +27 kJ
A positive enthalpy means the reaction is
endothermic because the reactants have
gained energy. Heat has been absorbed.
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Stoichiometry and Heat
Knowing the enthalpy of a reaction, we
can determine the heat given off or
absorbed by the given mass of a
reactant.
The molar coefficients are directly related
to the enthalpy.
Stoichiometry and Heat
2NaHCO3 + 85KJ  Na2CO3 + H2O + CO2
How much heat is required to decompose
2mol of sodium bicarbonate?
How much heat is required to decompose
4mol of sodium bicarbonate?
Stoichiometry and Heat
2C2H6 + 7O2  4CO2 + 6H20 +3120KJ
How much energy would be released
when 2mol of ethane reacts according to
the above equation?
How much energy would be released
when 18mol of water are formed according
to the above equation?
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Stoichiometry and Heat
Using the following equation:
2SO3 + 196KJ  2SO2 + O2
How much heat would be needed to
decompose 60g of SO3?
Stoichiometry and Heat
How much heat would be released when
1.48g of chlorine reacts with excess
phosphorus according to the following
equation:
2P + 5Cl2  2PCl5, ΔH = -886kJ
Stoichiometry and Heat
N2 + O2  2NO, ΔH = 180.6kJ
If 558KJ of energy are supplied, what
mass of NO can be made?
How much energy is required to form 78g
of NO?
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Section 3B Review
Energy &
Conversions
Endo or
Exo?
Heat
Fuel
Stoichiometry Additives
Labs &
Activities
Misc.
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