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Candle Wax Combustion
What Happens to Candle Wax When a Candle
Burns
The process involves an intricate chemical reaction
By Anne Marie Helmenstine, Ph.D.
When you
burn a candle, you end up with less wax after burning than you started with.
This is
because the wax oxidizes, or burns, in the flame to yield water and carbon
dioxide, which dissipate in the air around the candle in a reaction that also
yields light and heat.
Candle
Wax Combustion
Candle
wax, also called paraffin, is composed of chains of connected carbon atoms surrounded
by hydrogen atoms.
These
hydrocarbon molecules can burn completely.
When you
light a candle, wax near the wick melts into a liquid.
The heat
of the flame vaporizes the wax molecules and they react with the oxygen in the
air. As wax is consumed, capillary action draws more liquid wax along the wick.
As long
as the wax doesn't melt away from the flame, the flame will consume it
completely and leave no ash or wax residue.
Both
light and heat are radiated in all directions from a candle flame. About one-quarter
of the energy from combustion is emitted as heat.
The heat
maintains the reaction, vaporizing wax so that it can burn, melting it to
maintain the supply of fuel.
The
reaction ends when there is either no more fuel (wax) or when there isn't
enough heat to melt the wax.
Equation
for Wax Combustion
The exact
equation for wax combustion depends on the specific type of wax that is used,
but all equations follow the same general form.
Heat
initiates the reaction between a hydrocarbon and oxygen to produce carbon
dioxide, water, and energy (heat and light).
For a
paraffin candle, the balanced chemical equation is:
C25H52 +
38 O2 → 25 CO2 + 26 H2O
It's
interesting to note that even though water is released, the air often feels dry
when a candle or fire is burning. This is because the increase in temperature
allows air to hold more water vapor.
You're
Unlikely to Inhale Wax
When a
candle is burning steadily with a teardrop-shaped flame, combustion is
extremely efficient.
All that
is released into the air is carbon dioxide and water.
When you
first light a candle or if the candle is burning under unstable conditions, you
may see the flame flicker. A flickering flame may cause the heat required for
combustion to fluctuate.
If you
see a wisp of smoke, that's soot (carbon) from incomplete combustion.
Vaporized
wax does exist right around the flame but doesn't travel very far or last very
long once the candle is extinguished.
One
interesting project to try is to extinguish a candle and relight it from a
distance with another flame.
If you
hold a lit candle, match or lighter close to a freshly extinguished candle, you
can watch the flame travel along the wax vapor trail to relight the candle.
Anne Marie Helmenstine, Ph.D.
Chemistry Expert
Education
Ph.D., Biomedical Sciences, University of
Tennessee at Knoxville
B.A., Physics and Mathematics, Hastings
College
Introduction
Ph.D. in biomedical sciences from the
University of Tennessee at Knoxville - Oak Ridge National Laboratory.
Science educator with experience teaching
chemistry, biology, astronomy, and physics at the high school, college, and
graduate levels.
ThoughtCo and About Education chemistry
expert since 2001.
Widely-published graphic artist, responsible
for printable periodic tables and other illustrations used in science.
Experience
Anne Helmenstine, Ph.D. has covered chemistry
for ThoughtCo and About Education since 2001, and other sciences since 2013.
She taught chemistry, biology, astronomy, and physics at the high school,
college, and graduate levels. She has worked as a research scientist and also
abstracting and indexing diverse scientific literature for the Department of
Energy.
In addition to her work as a science writer,
Dr. Helmenstine currently serves as a scientific consultant, specializing in
problems requiring an interdisciplinary approach. Previously, she worked as a
research scientist and college professor.
Education
Dr. Helmenstine holds a Ph.D. in biomedical
sciences from the University of Tennessee at Knoxville and a B.A. in physics
and mathematics with a minor in chemistry from Hastings College. In her
doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and
medical diagnostic tests.
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