Maddie James
Does a candle need oxygen to burn? Yes, a candle requires oxygen to burn. This is because fire is a chemical reaction that produces light and heat from oxygen and fuel. In a simple experiment, placing a glass jar over a candle will cause the flame to go out as it uses up the oxygen inside the jar. However, there are exceptions, such as chlorate candles, which when burned, release oxygen in emergency situations, such as in submarines.
| Characteristics | Values |
|---|---|
| Definition | An ignitable wick embedded in wax or another flammable solid substance such as tallow that provides light, heat, scent, or a method of keeping time. |
| Composition | Wax, wick, and sometimes fragrance. |
| Types of Wax | Paraffin wax, beeswax, soy, coconut, apricot, vegetable, etc. |
| Types of Wick | Natural fibres like cotton or glass fibre. |
| History | Candles have been used for over two millennia. |
| Uses | Functional, symbolic, aesthetic, and cultural or religious purposes. |
| Combustion | The process of burning a candle involves the chemical reaction of combustion, which creates heat, light, water vapour, and carbon dioxide. |
| Temperature | The temperature of a candle flame varies, with the hottest part reaching approximately 1400°C. |
| Smoke | Smoke is caused by unburned carbon particles that have escaped from the flame due to incomplete combustion. |
| Scent | The strength of a candle's scent depends on its size, how much wax has melted, and the length of burning time. |
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What You'll Learn
How does a candle work?
A candle is an ignitable wick embedded in wax or another flammable solid substance, such as tallow, that provides light and, in some cases, fragrance. The wick of a candle is lit, and the heat melts the wax, which vaporises and combines with oxygen in the air to form a flame. The flame then melts the top of the mass of solid fuel, which moves upward through the wick via capillary action to be continually burnt, thereby maintaining a constant flame. The candle shortens as the solid fuel is consumed, and the wick shortens with it.
The wick of a candle needs to be naturally absorbent so that it can easily draw the wax and fragrance. The candle wick acts as an absorbent, pulling the liquid wax up and through the wick as it touches the flame. The lighted wick begins to heat up the wax and turn it into liquid. The liquid wax then gets absorbed by the wick and vaporises it. The wax vapour burns and keeps the candle lit.
A candle flame has a wide range of temperatures in a relatively small space. The blue area at the base of the flame is oxygen-rich, and this is where the hydrocarbon molecules vaporise 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 molecules rise, they continue to heat until they ignite and emit a full spectrum of visible light. The yellow portion of the spectrum is the most dominant when the carbon ignites, so the human eye perceives the flame as yellowish.
Candles are a crude example of an incandescent lamp, which converts the hydrocarbons in wax into carbon dioxide and water through the chemical reaction known as combustion.
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What is a candle made of?
A candle is a mass of wax or another flammable solid substance, such as tallow, containing an ignitable wick. When lit, the heat of the flame melts the wax near the wick, which then moves upward through the wick via capillary action and is burned, maintaining a constant flame.
Candles have been made from a variety of materials over the centuries, including beeswax, whale fat, and tallow. Beeswax candles were historically expensive and limited to elite and church use. Tallow was a cheaper alternative, but it produced an unpleasant smell and smoke. In the modern era, candles are often made from paraffin wax, a petroleum byproduct derived from the refining of crude oil. Paraffin wax is the most commonly used candle wax today due to its affordability and efficient production techniques.
Other types of waxes used in candle-making include soy wax, palm wax, gels, and synthesized waxes. Soy wax is a vegetable wax made from soybean oil, offering a renewable and environmentally friendly alternative to paraffin wax. Coconut wax is another option, known for its slow and even burning, strong fragrance, and sustainability. However, it is more expensive and softens easily in warm temperatures, making it difficult to work with.
The wick of a candle is typically made from absorbent materials such as cotton or hemp, or materials with strong capillary action, like glass fiber. The type of wax and the size of the wick affect the burn rate of a candle, with larger wicks and certain waxes, like beeswax, resulting in a slower burn.
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What happens when you blow out a candle?
When you blow out a candle, a stream of white smoke is released from the wick. This smoke is paraffin wax in vapour form, which is hot enough to relight. If you touch a lit match to the stream, the flame will run down and relight the wick. The wick does not burn because the vapourising wax cools it and protects it. This is similar to the camping trick of boiling water in a paper cup—the cup does not burn because the water inside cools it.
The flame of a candle is a very efficient combustion machine. The wick of a candle is lit, and the heat melts and ignites a small amount of solid fuel (wax), which vaporises and combines with oxygen in the air to form a flame. The flame then melts the top of the mass of solid fuel, which moves upward through the wick via capillary action to be continually burnt, thereby maintaining a constant flame. The candle shortens as the solid fuel is consumed, and the wick shortens with it.
The lighted wick begins to heat up the wax and turn it into liquid. The liquid wax is then absorbed by the wick and vaporised. The wax vapour burns and keeps the candle lit. The heat of the flame vaporises the liquid wax, turning it into a hot gas. As the hot gas rises, cooler air and oxygen are pulled in at the bottom of the flame to replace it. The oxygen-rich blue zone at the base of the flame is where the hydrocarbon molecules vaporise and start to break apart into hydrogen and carbon atoms. The hydrogen is the first to separate and reacts with the oxygen to form water vapour. Some of the carbon burns here to form carbon dioxide.
The colour of the candle flame is yellow because, as the carbon ignites, the yellow portion of the spectrum is the most dominant, so the human eye perceives the flame as yellowish. The blue part of the flame is where the wax burns cleanly with lots of oxygen, and the smoke is made in the bright yellow part of the flame, where there is incomplete combustion. The smoke is an aerosol of tiny particles of solid, unburned carbon from the wax mixed with steam.
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How do candles burn in space?
Candles can burn in space, but the flame behaves differently than on Earth. The process of combustion that allows a candle to burn on Earth is influenced by gravity, which pulls cooler, denser air downwards, while hotter, less dense air rises. This movement creates a flow of fresh oxygen towards the flame, allowing combustion to continue.
In space, the lack of gravity alters the behaviour of combustion. Without gravity to create airflow, the supply of oxygen to the flame is limited. This oxygen supply comes from random molecular motion, called diffusion. As the oxygen molecules move towards the flame, they form a uniform sphere of gas around it. The spherical flame burns at a lower temperature and with a weaker, bluer colour than on Earth. This is because the flame contains fewer soot particles, which emit a yellow light when heated.
The unique spherical shape of flames in space is a direct result of the lack of gravity, which also influences the supply of oxygen and the movement of gases around the flame. In microgravity, candle flames take on a spherical shape instead of the teardrop shape seen on Earth. This is because the hot air around the flame does not rise, and there is no flow of fresh oxygen towards the flame.
Experiments conducted by NASA in the late 1990s and observations from the Mir Space Station have provided valuable insights into the behaviour of candle flames in microgravity. These studies have practical applications for space travel and human habitation in space, such as improving fire safety measures and designing better fire suppression systems. Additionally, understanding combustion in space can lead to more efficient and cleaner combustion processes on Earth, benefiting industries like energy production and transportation.
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Are candles bad for your health?
Candles have been used for over two millennia for light, heat, fragrance, and celebrations. While they are no longer essential for illumination, they are still commonly used for functional, symbolic, and aesthetic purposes.
Burning candles does release chemicals and increases indoor air pollution. However, there is little scientific evidence that candles are a danger to your health. As long as you are taking the proper fire safety precautions, the effects, if any, are minimal.
The risk of indoor air pollution is lower if the space is well-ventilated. Burning candles in a ventilated room minimizes the smoke you breathe in. According to Dr. Sobia Farooq, a staff pulmonologist at the Cleveland Clinic, the amount of indoor air pollution caused by burning candles is nowhere near the amount from a wood-burning fireplace or wood stove.
There is a concern that extended exposure to particulate matter can lead to heart and lung problems. Candles made from natural sources, such as palm stearin, beeswax, or soy wax, are the best option for minimizing the amount of particulate matter you breathe in. These candles release the least dangerous chemicals and produce less soot than paraffin candles.
Some candles contain wicks with lead or metal, which can produce dangerous emissions and cause lead poisoning. However, many countries have taken action to prevent the use of lead and metal-cored candle wicks.
Overall, while burning candles does increase indoor air pollution, the risk to your health is minimal, especially in well-ventilated spaces.
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Frequently asked questions
Yes, a candle produces light through combustion. The flame of a candle is an example of what is known as incandescent light.
Yes, a candle releases heat through combustion. Approximately one-fourth of the energy created by a candle's combustion is given off as heat.
Yes, a candle releases chemicals such as volatile organic compounds, carbon dioxide, and toxic gases.
Yes, a candle can release fragrance. When the molecules of the fragrance are heated, they emit an aroma. The strength of the scent will change depending on the length of time the candle is burned.
