Transcript Endothermic vs_ Exothermic

• Thick liquid consisting of
hundreds of combustible
hydrocarbons with small
amounts of sulfur,
oxygen, and nitrogen
• Dead organic matter from
plants and animals piled
up on the sea floor
hundreds of millions of
years ago
• Who has it?
Middle East-Saudi
Arabia, Iraq, Kuwait,
Iran, United Emigrates,
Venezuela
OPEC-ORGANIZATION OF PETROLEUM
EXPORTING COUNTRIES
Energy is the Ability To Do Work
Types of Energy?
Energy
Kinetic
energy
(EK)
Energy due
to motion
Potential
energy
(EP)
Energy due to
position (stored
energy)
Electrical
What is Mechanical Energy?
o
Energy due to a object’s motion (kinetic) or position
(potential).
The bowling ball has mechanical energy.
When the ball strikes the pins, mechanical energy is
transferred to the pins!
What is Light Energy?
Light energy is electromagnetic radiation,
particularly radiation of a wavelength that
is visible to the human eye. The movement
of photons.
Includes energy from gamma rays, x-rays,
ultraviolet rays, visible light, infrared rays,
microwave and radio bands
What is Electrical Energy?
o
Energy caused by the movement of electrons
o
Easily transported through power lines and
converted into other forms of energy
What is Chemical Energy?
Energy that is available for release
from chemical reactions.
The chemical bonds in a
matchstick store energy that is
transformed into thermal energy
when the match is struck.
What is Heat Energy?
o The heat energy of an object
determines how active its atoms
are. This causes a change in
temperature.
A hot object is one whose atoms and
molecules are excited and show
rapid movement.
A cooler object's molecules and
atoms will show less movement.
Nuclear energy is the
energy stored in the nucleus
of an atom.
Submarines, power plants,
and smoke detectors all use
nuclear energy. Nuclear
power plants use uranium,
a radioactive element, to
create electricity.
THERMOCHEMISTRY
The study of heat released or required by
chemical reactions
Fuel is burnt to produce energy - combustion (e.g. when
fossil fuels are burnt)
CH4(g) + 2O2(g)
CO2(g) + 2H2O(l) + energy
Reactions
All chemical reactions either release or absorb heat
Exothermic reactions:
Reactants
products + energy as heat
e.g. burning fossil fuels
Endothermic reactions:
Reactants + energy as heat
e.g. photosynthesis
products
Endothermic and exothermic reactions
Step 1: Energy must be
SUPPLIED to break bonds:
Step 2: Energy is RELEASED
when new bonds are made:
A reaction is EXOTHERMIC if more energy is RELEASED
then SUPPLIED. If more energy is SUPPLIED then is
RELEASED then the reaction is ENDOTHERMIC
Measuring Heat
reaction
reaction
Exothermic reaction, heat
given off & temperature of
water rises
Endothermic reaction, heat
taken in & temperature of
water drops
Vaporization
Energy has to be supplied to a liquid to enable it to overcome
forces that hold molecules together
• endothermic process
Melting
Energy is supplied to a solid to enable it to vibrate more
vigorously until molecules can move past each other and flow
as a liquid
• endothermic process
Freezing
Liquid releases energy and allows molecules to settle into a
lower energy state and form a solid
• exothermic process (we remove heat from water when
making ice in freezer)
Energy
level
Energy level diagrams
Activation
energy
Reactants
Using a catalyst
might lower the
activation energy
Energy given
out by
reaction
Products
Reaction progress
Exothermic vs endothermic:
EXOTHERMIC – more
energy is given out than is
taken in (e.g. burning,
respiration)
ENDOTHERMIC –
energy is taken in but
not necessarily given out
(e.g. photosynthesis)
Burning Methane
CH4 + 2O2
2H2O + CO2
Methane
Oxygen
Carbon dioxide
Water
Bond Energies
C-H = 435 Kj
O=O = 497 Kj
Total for breaking bonds = 4x435 + 2x497 = 2734 KJ/mol
C=O = 803 Kj
H-O = 464 Kj
Total for making bonds = 2x803 + 4x464 = 3462 KJ/mol
Total energy change = 2734-3462 = -728 KJ/mol
Drawing this on an energy diagram:
2734 Kj
3462 Kj
-728 Kj
More energy is given out (3462) than is given in (2734) –
the reaction is EXOTHERMIC. The total (“nett”) energy
change is –728 Kj. An endothermic reaction would have a
positive energy change.
ENERGY CONVERSIONS
EXAMPLE-PRODUCING POWER from Coal
FOSSIL FUELS (POTENTIAL ENERGY)
POWER PLANT (THERMAL ENERGY)
GENERATOR TURBINE (MECHANICAL ENERGY)
ELECTRICAL TRANSMISSION LINES (ELECTRICAL ENERGY)
Law of Conservation of Energy-energy is not created nor destroyed