Ben Carter
Candles are made up of three essential components: the wick, wax, and fragrance. The wick is usually made of cotton, and it draws the liquid wax up through capillary action. The wax is a hydrocarbon, meaning it is primarily composed of hydrogen and carbon atoms. When a candle burns, the hydrogen and carbon atoms in the wax combine with the oxygen in the air to form carbon dioxide and water vapour. The carbon atoms can also form soot, which is the cause of the flame's yellow colour.
| Characteristics | Values |
|---|---|
| Composition of candle wax | Hydrogen and carbon atoms |
| Hydrocarbons | |
| Hydrocarbon molecules | |
| Straight-chain hydrocarbons | |
| Hydrogen | |
| Carbon | |
| Oxygen | |
| Nitrogen | |
| Water vapour | |
| Carbon dioxide | |
| Soot | |
| Unburnt carbon particles | |
| Fragrance | |
| Wick composition | Cotton |
| Metal | |
| Lead | |
| Organic cotton |
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What You'll Learn
The chemical reaction of combustion
Candles are made of hydrocarbons, which are molecules composed of hydrogen and carbon atoms. When a candle burns, it undergoes a process of combustion, which is a chemical reaction that produces heat and light.
The first step in the combustion process is the vaporization of the solid wax. The heat of the flame melts the wax, and the liquid wax is drawn up through the wick by capillary action. Once the wax reaches the top of the wick, it vaporizes and mixes with oxygen in the air, initiating the combustion reaction.
In the combustion reaction, the hydrocarbon molecules break apart into hydrogen and carbon atoms. The hydrogen atoms react with oxygen in the air to form water vapour. Some of the carbon atoms burn and react with oxygen to form carbon dioxide. This process occurs in the oxygen-rich blue zone at the base of the flame.
Above the blue zone is a small dark orange-brown section where the carbon atoms continue to break down and form hardened carbon particles, or soot. As these carbon particles rise, they are heated to high temperatures, causing them to ignite and emit light. The yellow colour of the flame is due to the hot soot particles emitting black-body radiation.
The shape of the flame is influenced by the convection currents created as the warm air around the flame rises and is replaced by cooler air and oxygen. This cycle of upward-moving air gives the flame its characteristic teardrop shape. The combustion process in a candle is a self-sustaining one, with the heat generated melting more wax to fuel the reaction until the fuel or heat source is depleted.
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The role of oxygen in combustion
The combustion process of a candle involves a chemical reaction between a fuel source and an oxidant, which is usually atmospheric oxygen. This process produces oxidized gaseous products, including carbon dioxide, water vapour, and energy in the form of heat and light.
Oxygen plays a crucial role in the combustion of a candle. Firstly, it is essential for the initiation of the combustion reaction. The wax in a candle, typically made of hydrocarbons, requires sufficient oxygen from the surrounding air to burn. As the flame heats the air, it starts to rise, creating an upward moving cycle of air around the flame known as a convection current. This cycle ensures a continuous supply of oxygen to the flame, sustaining the combustion process.
In the combustion reaction, the hydrocarbon molecules in the candle wax vaporize and break apart into hydrogen and carbon atoms. The hydrogen atoms react with the oxygen in the air to form water vapour. Simultaneously, some of the carbon atoms burn, combining with oxygen to produce carbon dioxide. This process releases energy in the form of heat and light, contributing to the flame of the candle.
The colour of the candle flame is also influenced by the presence of oxygen. The base of the flame, known as the oxygen-rich blue zone, is where the hydrocarbon molecules break down. Here, hydrogen reacts with oxygen, forming water vapour. The dark orange-brown region above it has relatively less oxygen, and this is where carbon continues to break down, forming soot particles. These soot particles, when heated, ignite and emit a yellowish light, giving the candle flame its characteristic colour.
Additionally, oxygen plays a role in the potential incomplete combustion of a candle. If the flame receives an inadequate amount of oxygen or fuel, it may flicker or flare. This instability can lead to the escape of unburned carbon particles, known as soot, from the flame before they can fully combust. Therefore, a stable and efficient combustion process in a candle relies on the proper balance of oxygen and fuel, ensuring the complete combustion of the wax and minimising the release of unburned particles.
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The different colours of the flame
The colour of a candle flame is typically yellow, but it can sometimes appear orange, blue, or even red. The colour of the flame depends on the temperature and oxygen levels in the burning candle.
The blue zone at the base of the flame is where the hydrocarbon molecules vaporize and start to break apart into hydrogen and carbon atoms. The hydrogen reacts with the oxygen to form water vapour, and some of the carbon burns to form carbon dioxide. This blue zone is the hottest part of the flame, reaching temperatures of around 1400° C.
Above the blue zone is a small dark orange-brown section, where there is relatively little oxygen. Here, the various forms of carbon continue to break down and form hardened carbon particles (soot), which rise along with the water vapour and carbon dioxide from the blue zone.
As these particles reach the bottom of the yellow zone, the formation of carbon (soot) particles increases. As they rise and continue to heat up, they eventually ignite and emit a full spectrum of visible light. The yellow portion of the spectrum is the most dominant when the carbon ignites, which is why we perceive the flame as yellowish.
While it is challenging to colour the flames of wax candles, it is possible to create coloured flames using metal salts or chemicals. For example, copper chloride can be suspended in petroleum jelly or dissolved in water and used to soak wicks, resulting in a blue flame.
In addition to the scientific explanations for the different flame colours, some people also associate certain meanings and symbolism with the colours of candle flames. For instance, a white candle flame may represent purity and healing, while a red flame could signify danger or passion.
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The production of carbon dioxide and water vapour
Firstly, the heat of the flame melts the solid wax, turning it into a liquid state. This liquid wax is then drawn up through the wick by capillary action, where it vaporizes and turns into a hot gas. The vaporized wax molecules, which contain hydrogen and carbon atoms, rise into the flame and encounter oxygen from the surrounding air.
In the oxygen-rich blue zone at the base of the flame, the hydrocarbon molecules begin to break apart into hydrogen and carbon atoms. The hydrogen atoms react with the oxygen to form water vapour. Simultaneously, some of the carbon atoms combine with oxygen to form carbon dioxide. This process releases energy in the form of heat and light, contributing to the flame's teardrop shape and yellowish colour.
As the carbon dioxide and water vapour rise, they encounter a region of the flame with relatively little oxygen, known as the dark or orange-brown region. Here, the carbon atoms continue to break down and form small, hardened particles of soot. These soot particles are heated to high temperatures, reaching approximately 1000 degrees Centigrade, and eventually ignite, emitting a full spectrum of visible light. The dominance of the yellow portion of the spectrum in this process is what gives the candle flame its characteristic yellowish appearance.
The carbon dioxide and water vapour produced by the burning candle cool and mix with the surrounding air, becoming indistinguishable from other molecules. Over time, these molecules disperse into the atmosphere, and within about a year, they can spread around the globe. While carbon dioxide and water vapour are normal components of the air at low levels, they can become dangerous in higher concentrations.
The chemical equation for wax combustion varies depending on the specific type of wax used, but it generally involves the reaction between hydrocarbons and oxygen, resulting in the production of carbon dioxide, water, and energy in the form of heat and light. The efficiency of this combustion process depends on factors such as airflow and the stability of the flame, with a steady teardrop-shaped flame indicating optimal combustion.
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The structure of candle wax
Candle wax is a fascinating substance with a long history. It is solid at room temperature but becomes liquid at higher temperatures, and this property forms the basis of its use in candles. When a candle is lit, the heat of the flame melts the wax near the wick, and this liquid wax is drawn up the wick by capillary action.
The chemical composition of candle wax is CnH2n+2, where 'n' represents the number of carbon atoms, which can vary. Candle wax is primarily a hydrocarbon, composed of hydrogen and carbon atoms. These atoms are released when the wax vapourises and the hydrocarbon molecules break apart.
The type of wax used in candle-making can vary, and over the centuries, candle waxes have been developed from a variety of fats, oils, and waxy substances derived from animals, insects, plants, and even rocks. The development of new waxes has typically depended on the availability of raw materials and the ease of processing them into a suitable form. For example, beeswax was introduced to Europe in the Middle Ages but was rarely used in homes due to its expense. In contrast, tallow, rendered from animals, was the typical everyday candle wax used in Europe and the Americas until the 18th century when the whaling industry stimulated the development of spermaceti wax.
Today, the most commonly used candle wax is paraffin, a straight-chain hydrocarbon developed by removing the naturally-occurring waxy substance from petroleum during refining. Other types of waxes used in candle-making include beeswax, soy wax, palm wax, gels, and synthetic waxes.
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Frequently asked questions
A candle's wax typically consists of hydrocarbons, meaning they are primarily composed of hydrogen and carbon atoms.
The heat of the flame melts the wax, which is then drawn up the wick. The heat of the flame then evaporates the liquid wax, turning it into a hot gas.
The blue part of the flame is where wax burns cleanly with lots of oxygen, producing carbon dioxide and water vapour.
The yellow part of the flame is where there is a lower amount of oxygen, so carbon particles only partially burn, producing light and smoke.
The black region at the bottom of the flame is caused by the presence of unburnt wax vapours. This is where hydrocarbon molecules evaporate and begin to break down into carbon and hydrogen atoms.
