Jessie Taylor
Burning candles produce carbon dioxide (CO2) and water vapour (H2O) as a result of a combustion reaction between the candle's wax and oxygen. The wax, which is largely composed of hydrogen and carbon atoms, melts and vaporises as heat is applied from the flame. The vaporised wax then reacts with oxygen from the air, producing carbon dioxide and water vapour, along with heat and light energy. This combustion reaction can be summarised by the chemical equation: CxHy + O2 → CO2 + H2O. While carbon dioxide from candle combustion is not directly toxic, it can contribute to poor indoor air quality and health complaints if not properly ventilated.
| Characteristics | Values |
|---|---|
| Carbon dioxide formed when a candle combusts | Yes |
| Chemical reaction | Wax and oxygen combine to produce carbon dioxide and water vapour |
| Chemical equation | CxHy+O2→CO2+H2O |
| Other gases produced | Carbon monoxide, nitrogen oxides, formaldehyde, benzene, toluene, acetaldehyde, fragrance chemicals |
| Health concerns | Exposure to carbon dioxide and other gases may lead to cardiovascular and respiratory issues |
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What You'll Learn
Carbon dioxide is formed when wax and oxygen combine
When a candle burns, it undergoes a combustion reaction, creating carbon dioxide and water vapour. This occurs when the wax, a hydrocarbon composed of hydrogen and carbon atoms, combines with oxygen in the air.
The heat of the flame melts the wax near the wick, and this liquid wax is drawn up the wick by capillary action. The heat then vaporises the liquid wax, breaking down the hydrocarbons into molecules of hydrogen and carbon. These vapour molecules are drawn up into the flame, where they react with oxygen from the air to create heat, light, water vapour, and carbon dioxide.
The blue area at the base of the flame is oxygen-rich, and this is where the hydrocarbon molecules vaporise and begin to break apart into hydrogen and carbon atoms. The hydrogen is the first to separate here. Above this is a small dark orange-brown section, where various forms of carbon continue to break down and small, hardened carbon particles begin to form. As they rise, they are heated to approximately 1000 degrees Centigrade. At the bottom of the yellow zone, the formation of carbon (soot) particles increases, and as they rise, they ignite to incandescence, emitting a full spectrum of visible light.
The carbon dioxide and water vapour produced by the burning candle will cool and mix into the air in the room, becoming indistinguishable from other molecules of carbon dioxide and water. Over the next few hours, as the air in the room is exchanged with outdoor air, the molecules from the candle will escape and begin to disperse.
The chemical equation for the combustion of a candle, typically composed of paraffin wax, is as follows: C₂₅H₅₂ + 38O₂ ------> 25CO₂ + 26H₂O. This illustrates that for every molecule of wax, 38 molecules of oxygen are required to form 25 molecules of carbon dioxide and 26 molecules of water.
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The wax melts and vaporises, reacting with oxygen
When a candle burns, it undergoes a combustion reaction, which is a chemical process where a substance reacts with oxygen, releasing energy in the form of light and heat. This combustion reaction involves the wax and oxygen to produce carbon dioxide, water, and energy.
The wax of the candle melts and vaporizes as heat is applied from the flame. The heat of the flame melts the wax near the wick. This liquid wax is then drawn up the wick by capillary action. The heat of the flame vaporizes the liquid wax, turning it into a hot gas. The vaporized wax then reacts with oxygen from the air to combust into a flame.
The vaporized wax molecules are drawn into the flame, where they react with oxygen from the air to create heat, light, water vapour, and carbon dioxide. The oxygen-rich 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 is the first to separate and reacts with the oxygen to form water vapour. Some of the carbon burns here to form carbon dioxide.
As the candle burns, the flame heats the nearby air and starts to rise. As this warm air moves up, cooler air and oxygen rush in at the bottom of the flame to replace it. This creates a continual cycle of upward-moving air around the flame (a convection current), which gives the flame its elongated or teardrop shape. Over time, the CO₂ and water vapour produced by the candle cool and mix into the air in the room, becoming indistinguishable from any other molecule of CO₂ or water.
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The flame gives off carbon dioxide and water vapour
The combustion of a candle involves a chemical reaction between the candle's wax and oxygen in the air. The wax is a hydrocarbon, largely composed of hydrogen and carbon atoms. 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 flame then vaporises the liquid wax, breaking down the hydrocarbons into hydrogen and carbon atoms.
These vaporised molecules react with oxygen from the air, creating heat, light, water vapour, and carbon dioxide. The carbon dioxide and water vapour then cool and mix into the room's air, becoming indistinguishable from other molecules. Over time, as the room's air is exchanged with outdoor air, the molecules from the candle flame escape the room and begin to disperse.
The blue area at the base of the flame is oxygen-rich, and this is where the hydrocarbon molecules vaporise and begin to break apart into hydrogen and carbon atoms. Above this is a small dark orange-brown section, where various forms of carbon continue to break down, and small, hardened carbon particles (soot) begin to form. As they rise, along with the water vapour and carbon dioxide, they are heated to approximately 1000 degrees Centigrade.
The flame of a candle is an efficient combustion machine, but if it receives too little or too much air or fuel, it can flicker or flare, and unburned carbon particles (soot) will escape from the flame before they can fully combust. The wisps of smoke sometimes seen when a candle flickers are caused by these unburned soot particles escaping from the flame due to incomplete combustion.
The amount of carbon dioxide and water vapour produced by a candle is relatively small and comparable to the amount exhaled by another person in the room. However, constant exposure to these particles can lead to cardiovascular and respiratory issues. Therefore, it is recommended to ensure proper ventilation when burning candles, especially scented or paraffin candles, which can release additional chemicals and pollutants.
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Carbon dioxide is heavier than air
When a candle burns, the heat of the flame melts the wax near the wick. The liquid wax is then drawn up the wick and vapourised by the heat of the flame, breaking down the hydrocarbons into molecules of hydrogen and carbon. These vapourised molecules react with oxygen from the air, creating heat, light, water vapour, and carbon dioxide.
The combustion of candle wax releases energy in the form of heat and light, with approximately one-fourth of the energy given off as radiant heat. The flame of a candle has distinct zones, each with its own characteristics. The blue zone at the base is oxygen-rich, where hydrocarbon molecules vapourise and break apart into hydrogen and carbon atoms. Above this is a small dark orange-brown section, where various forms of carbon continue to break down and form small, hardened carbon particles. As these particles rise, they are heated to high temperatures, and when they reach the yellow zone, they ignite and emit a full spectrum of visible light. The fourth zone, sometimes called the veil, is the faint outside blue edge that extends from the base of the flame.
While candles can add ambiance and fragrance to a room, it is important to be mindful of the potential health risks associated with their combustion by-products. The carbon dioxide and water vapour produced by burning candles can be dangerous at high levels. To minimise exposure to airborne particles, it is recommended to ensure proper ventilation and opt for clean, white candles with fewer additives.
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Carbon dioxide is not toxic but can impact air quality
When a candle burns, it releases carbon dioxide and water vapour. The carbon dioxide formed when a candle burns is not toxic, but it can impact air quality.
Carbon dioxide is a colourless, odourless gas that is produced both naturally and through human activities, such as burning gasoline, coal, oil, and wood. While carbon dioxide is not directly toxic, it can impact air quality and cause health issues when present in high concentrations. Indoor carbon dioxide levels can be influenced by the number of occupants, the size of the room, ventilation, and the presence of combustion by-products.
The main way people are exposed to carbon dioxide is through the air. In indoor environments, carbon dioxide levels can be measured to assess ventilation and air quality. While carbon dioxide itself may not be the primary cause of indoor air quality issues, insufficient ventilation can lead to the buildup of contaminants and carbon dioxide, resulting in potential discomfort and health symptoms.
In areas with proper ventilation, carbon dioxide concentrations are typically below 1000 parts per million (ppm) and are acceptable to most individuals. However, at levels above 5000 ppm, carbon dioxide can cause health issues such as headaches, dizziness, nausea, and difficulty breathing. Prolonged exposure to extremely high levels of carbon dioxide, such as around 40,000 ppm, can lead to asphyxiation as it replaces oxygen in the blood.
While the amount of carbon dioxide produced by a candle is relatively small, burning multiple candles or in enclosed spaces without adequate ventilation can increase carbon dioxide levels and impact air quality. Therefore, it is important to ensure proper ventilation when burning candles to maintain healthy carbon dioxide levels and overall air quality.
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Frequently asked questions
Yes.
Water vapour, carbon monoxide, nitrogen oxides, formaldehyde, benzene, toluene, acetaldehyde, and fragrance chemicals.
They are heavier than air, so they push the oxygen and other molecules in the air out of the way as they sink down over the flame and candle.
The flame goes out.
Approximately one year.
