WHEN A CANDLE BURNS, BOTH PHYSICAL AND CHEMICAL CHANGES OCCUR. WHAT ARE THESE CHANGES?
THIS A QUESTION BASED ON CHEMISTRY.
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The physical changes or actions that take place during burning of a candle include the following:
- Melting of the wax by the heat of the flame of candle. The melted wax forms a pool at the top of the wax column of the candle.
- Liquid candle seeping up the wick of the candle by capillary action. As the liquid wax gets seeps up the wick the level of the liquid pool of wax gets lowered and then more wax is liquified to continuously replenish the wax being sucked up the wick.
- Liquid wax at the tip of the candle being vaporized by the heat of the flame. It is this vaporised wax that burns in the candle to produce heat and light.
- Heating of the particles produced by burning of the candle, causing them to glow and radiate light.
It is interesting to note that the vaporization of the wax in the wick keeps the temperature of the wick and area immediately surrounding it comparatively cooler. As a result, the wick itself is not burnt down by the heat of candle flame.
The chemical action produced in burning of candle is the oxidation of the wax, which is composed of mixture of several different hydrocarbon compounds. In this process of oxidation, the hydrocarbons combine with the oxygen in the atmosphere to produce carbon-dioxide (CO2) and water (H2O). This chemical reaction also produces heat required for the physical changes described above..
the heat of thecandle flame first melts the wax, and it rises up the candle wick by capillary action. Farther up the wick, the greater heat vaporizes the wax molecules, which move from the wick into the surrounding space. The heat of
the flame and reactive molecules (free radicals) in the flame break apart the wax molecules, in particular stripping hydrogen atoms from the carbon-chain backbone. Some of the carbon chains fragment into gaseous carbon (C2) and into small (typically two-carbon atom containing) molecules
and molecular fragments. The hydrogen atoms stripped from the
eventually combine with oxygen atoms from the air to form water molecules.The carbon atoms eventually combine with oxygen to form carbon monoxide and carbon dioxide, but first many of them combine to form very large (as far as
molecules are concerned) clumps of carbon-rich solid material, called soot.Some of this soot burns to make carbon dioxide in the candle flame, and
sometimes some of it escapes the flame.* Several zones of a candle flame can be seen with the eye. At the bottom
is a region that gives off blue light. This light is actually molecular emission from gaseous carbon, C2. Further up the flame is a region that is substantially opaque and which gives off yellow light. This is known as the
"incandescent region", and is where hot soot particles glow,
light like the filament of a light bulb. The inside part of the flame, near
the wick, is oxygen-deficient, and most of the reactions that occur are
heat-induced fragmentations and rearrangements. In the outer regions, where
oxygen can enter from the surrounding air, the fragments combine with
oxygen, eventually forming water and carbon dioxide.
The Physical change: The physical change is that the wax melts because of the gas heat in the fire and the candle gets smaller and smaller as the candle melts.
When a candle burns, fuel (wax) is converted to vapours, the vapours mix with oxidizer (oxygen from air) when sufficient heat is provided the wick of catches the flame wherein radicals forms during the oxidation of fuel generates a chain reaction to sustain that fire. In other words wax which is hydrocarbon burns in air to form carbon dioxide & water. Whereas incomplete combustion results in carbon mono oxide in addition to former products. aromatic hydrocarbon such as wax when burnt also produces soot.
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