Jessie Taylor
Candles have been used for over two millennia, and while they are no longer essential for illumination, they are still commonly used for functional, symbolic, and aesthetic purposes. The science behind candles is fascinating, and the process by which a candle burns is a chemical reaction that turns solid wax into gas. This process, known as combustion, involves the heat of the flame, the presence of oxygen, and fuel. The heat of the flame melts the wax near the wick, which is then absorbed by the wick and pulled upward. The heat vaporizes the wax, and it is this wax vapour that burns, reacting with oxygen in the air to form a flame. This combustion reaction turns the solid wax into invisible carbon dioxide gas and water vapour.
| Characteristics | Values |
|---|---|
| What happens when a candle is lit? | The heat melts and ignites the wax, which vaporizes and combines with oxygen in the air to form a flame. |
| What is the flame made of? | The flame is made of carbon dioxide, water vapour, and light and heat energy. |
| What is the function of the wick? | The wick draws the melted wax or fuel upwards towards the flame through capillary action. |
| What is the role of oxygen? | In the oxygen-rich blue zone, hydrocarbon molecules (wax) vaporize and break apart into hydrogen and carbon atoms. |
| What is the yellow/orange zone? | This zone has less oxygen and is where carbon particles form and rise, heating up to 1000 degrees Centigrade. |
| What happens when the carbon ignites? | The flame is perceived as yellowish due to the dominance of the yellow portion of the spectrum. |
| What is the wax made of? | All waxes are hydrocarbons, composed of hydrogen and carbon atoms. |
| What type of waxes are used? | Beeswax, coconut wax, paraffin wax, and soy wax are common types. |
| What is the burn rate dependent on? | The size of the flame and burn rate are controlled by the wick and the type of wax. |
| Are there health concerns? | Candles emit volatile organic compounds, including carbon, and can be unsafe if fragrances are inhaled at high doses. |
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What You'll Learn
Candle wax turns into gas through combustion
Candles have been used for over two millennia, and while they are no longer essential for illumination, they are still commonly used for functional, symbolic, and aesthetic purposes. The science behind how candles work is a fascinating interplay of chemistry and physics.
A candle is a simple construct: an ignitable wick embedded in wax or another flammable solid substance such as tallow. When a candle is lit, the heat melts and ignites the wax, which is a solid fuel. The wick, through capillary action, draws the melted wax or fuel upwards towards the flame. The heat of the flame then vaporizes the wax, turning it into a flammable gas vapor.
The vaporized wax reacts with oxygen in the air, forming a flame. This flame then melts the top layer of the solid fuel, which moves upward through the wick to be continually burned, thus maintaining a constant flame. The candle shortens as the solid fuel is consumed, and the wick shortens with it.
The combustion of the vaporized wax releases light, heat, carbon dioxide, and water vapor. The oxygen-rich blue zone is where the hydrocarbon molecules vaporize and break apart into hydrogen and carbon atoms. The hydrogen reacts with oxygen to form water vapor, and some of the carbon burns to form carbon dioxide. The carbon particles continue to break down in the orange/brown region, forming soot. As they rise, they are heated to approximately 1000 degrees Centigrade, and at the bottom of the yellow zone, they ignite and emit a full spectrum of visible light.
The kind of wax used in a candle affects the burn rate, with beeswax and coconut wax burning longer than paraffin or soy wax. The size of the flame and the corresponding rate of burning are also influenced by the candle wick.
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The gas produced is carbon dioxide and water vapour
The combustion process of lighting a candle involves the release of light, heat, carbon dioxide, and water vapour. The heat of the candle flame causes the wax near the wick to melt and ignite, turning it into a flammable gas vapour. This vapour then reacts with oxygen in the air to form a flame. The oxygen-rich blue zone is where hydrocarbon molecules vaporize and start to break apart into hydrogen and carbon atoms. The hydrogen is the first to separate here and reacts with the oxygen to form water vapour. Some of the carbon burns to form carbon dioxide.
As the candle continues to burn, the wax moves up through the wick and is burned, maintaining a constant flame. The candle shortens as the wax is consumed, and the wick shortens as well. The kind of wax used affects the burn rate, with beeswax and coconut wax burning longer than paraffin or soy wax.
The process of a candle burning involves the transformation of solid wax into invisible carbon dioxide gas and water vapour. This occurs through a combustion reaction involving the heat of the flame, oxygen, and fuel. The wax is vaporized and combusts into a flame, releasing carbon dioxide and water vapour.
The colour of the candle flame is influenced by the presence of various forms of carbon particles. In the orange or brown region of the flame, there is relatively little oxygen, and carbon particles begin to form. These particles are heated to high temperatures as they rise, causing them to ignite and emit a full spectrum of visible light. The yellow portion of the spectrum is the most dominant, which is why the human eye perceives the flame as yellowish.
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The wick's role is to draw melted wax to the flame
The wick of a candle is a vital component, influencing how the candle burns. It is usually made of braided cotton and works by capillary action, conveying ("wicking") the fuel to the flame. The wick draws the liquified wax up into the flame, where it vaporizes and combusts. This process is similar to how a paper towel absorbs water. The size of the wick is important, as it determines the amount of fuel brought to the flame. A larger wick will result in a larger flame and a faster-burning candle.
The candle wick is treated with flame-resistant solutions to prevent it from being destroyed by the flames and to improve the flow of wax. Common treatments include borax and salt, which are dissolved in water and used to soak the wicks. Stiffeners are also used to direct the wick upright, allowing it to stand out of the liquid wax and conduct heat downward, melting the wax more efficiently.
The type of wick used in a candle is important and depends on various factors such as the type of wax, the candle's size, shape, colour, and fragrance. Different styles and sizes of wicks are available to ensure the candle burns cleanly and properly. For example, square wicks are preferred for beeswax candles, while cored wicks use a core material to keep the wick straight and upright during burning.
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The wax vapour, not liquid wax, burns
The process of combustion in a candle involves the transformation of solid wax into invisible carbon dioxide gas and water vapour. This occurs through the heat of the flame, the presence of oxygen, and fuel. When a candle is lit, the heat melts a small amount of solid fuel (the wax) near the wick, which then moves upwards through the wick via capillary action to be burned. The heat of the flame vaporises the wax, and it is this wax vapour that burns, not liquid wax.
The wick of the candle plays a crucial role in the burning process. It absorbs the liquid wax and pulls it upwards. The exposed wick is protected from burning by the vaporising wax, which cools it down. The diameter, stiffness, fire resistance, and tethering characteristics of the wick also influence how the candle burns.
The vaporised wax combines with oxygen in the air to form a flame. This combustion reaction releases carbon dioxide and water vapour. The carbon dioxide molecules are heavier than air, so they sink down and push oxygen and other molecules away, which is why they can be used to extinguish a flame.
The type of wax used in a candle also affects the burn rate. For example, beeswax and coconut wax burn slower than paraffin or soy wax. All waxes are essentially hydrocarbons, composed mainly of hydrogen and carbon atoms. During combustion, these molecules break apart, with hydrogen reacting with oxygen to form water vapour, and carbon burning to form carbon dioxide.
The combustion process of lighting a candle releases light, heat, and volatile organic compounds, including carbon, into the environment. This has led to the development of non-toxic candles to prevent the release of harmful emissions.
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Candles emit volatile organic compounds
The potential health risks associated with VOCs in candles can be mitigated by choosing natural wax options, such as soy, beeswax, or coconut wax. These natural alternatives generally produce fewer harmful emissions. It is also recommended to avoid candles with synthetic fragrances and opt for those scented with natural essential oils. Proper wicks, such as cotton or wood wicks, should be used instead of those with metal cores, which can release heavy metals when burned. Trimming the wick before lighting can help reduce soot production. Burning candles in well-ventilated areas is important to disperse any pollutants and minimise potential harm.
Additionally, diffusers provide a natural and customisable way to scent your home without producing harmful byproducts like soot or VOCs. Essential oils, such as orange, peppermint, clove, and lavender, can be used in diffusers to disperse fragrance naturally. Certain houseplants, including lavender, jasmine, and rosemary, can also freshen the air while filtering out pollutants, enhancing indoor air quality.
While candles create a cosy atmosphere, offer soothing light, and fill a room with pleasant fragrances, it is important to be aware of the potential health risks associated with VOC emissions. By making informed choices and embracing natural alternatives, individuals can maintain a healthy and pleasant living environment while still enjoying the ambiance of candles.
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Frequently asked questions
Yes, when a candle is lit, the heat melts and ignites the wax, which vaporizes and combines with oxygen in the air to form a flame.
The process of lighting a candle involves the release of light, heat, carbon dioxide, and water vapour to fuel the flame. All waxes are essentially hydrocarbons, which means they are composed of hydrogen and carbon atoms. When a candle burns, the hydrocarbon molecules vaporize and break apart into hydrogen and carbon atoms.
The intense heat of the candle's flame causes the melted wax in the wick to vaporize, turning it into flammable gas vapour.
The combustion of a candle transforms the solid wax into invisible carbon dioxide gas and water vapour.
The size of the flame and the corresponding rate of burning are largely controlled by the candle wick. The type of wax also affects the burn rate, with beeswax and coconut wax burning slower than paraffin or soy wax.
