Maddie James
Burning a candle is a simple process, but it involves a series of chemical reactions and physical changes. When a candle is lit, the heat of the flame melts the wax, which is then drawn up the wick and vaporized. The vaporized wax combines with oxygen in the air, creating heat, light, water vapour, and carbon dioxide. The blue area at the base of the flame is the hottest part, where hydrocarbon molecules break apart into hydrogen and carbon atoms. The yellow region above it is perceived as such due to the ignition of carbon soot particles, which emit a full spectrum of visible light. The combustion process of a candle can be affected by factors such as airflow and fuel, and improper burning can lead to smoke and soot formation. Ensuring proper ventilation and following safety guidelines, such as trimming the wick, are important considerations when burning candles.
| Characteristics | Values |
|---|---|
| Physical change | Wax melts |
| Chemical change | Light and heat energy is produced |
| Difference between chemical and physical change | Physical changes can be measured and seen, chemical changes cannot |
| Reactants | Wax, oxygen |
| Products | Light, heat, water vapour, carbon dioxide |
| Simple word equation | Wax + oxygen -> light + heat + water vapour + carbon dioxide |
| Fuel | Wax |
| Effect of too much fuel | Flame flares up or starts a small fire |
| Effect of too little or too much air | Flame flickers or flares |
| Colour of flame | Blue, orange-brown, yellow |
| Temperature of blue zone | 1400o C |
| Temperature of yellow zone | 1200o C |
| Temperature of orange-brown zone | 1000o C |
| Effect of burning for too long | Carbon collects on wick, leading to an unstable wick and a dangerously large flame |
| Effect of not burning long enough | Creation of a "memory ring", leading to "tunneling" |
| Effect of constant exposure to particles | Cardiovascular and respiratory diseases |
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What You'll Learn
The wax melts and vapourises
When a candle is alight, the heat of the flame melts the wax near the wick. This is a physical change. The melted wax is drawn up the wick through capillary action. The heat of the flame then vaporises the liquid wax, turning it into a hot gas. This is the start of the chemical change, where hydrocarbons in the wax break down into hydrogen and carbon atoms.
The vapourised molecules are drawn into the flame, where they react with oxygen from the air. This reaction produces heat, light, water vapour, and carbon dioxide. The heat radiates in all directions, with enough escaping the flame to melt more wax and fuel the combustion process. The cycle of upward-moving air around the flame is known as a convection current, giving the flame its teardrop shape.
The blue area at the base of the flame is where the wax vapour first enters and reacts with oxygen. This is the hottest part of the flame, reaching temperatures of 1400° C (2552° F). Above this is a small dark orange-brown section, where carbon continues to break down and form hardened particles. As the carbon rises, it is heated to around 1000° C, and at the bottom of the yellow zone, the formation of soot particles increases. As these particles rise, they ignite and emit a full spectrum of visible light, with the yellow portion dominating our perception of the flame's colour.
The carbon particles continue to rise and oxidise near the top of the flame's yellow region, reaching temperatures of approximately 1200° C. The fourth zone of the candle flame is the faint blue veil extending from the base up the sides of the flame cone. This cycle continues as long as there is enough fuel and heat to sustain it.
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Hydrocarbons break down into hydrogen and carbon
When a candle is lit, 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. This is when the combustion reaction begins.
The combustion reaction is a chemical process where a substance reacts with oxygen, releasing energy in the form of light and heat. In the context of a burning candle, the wax, which is a hydrocarbon composed of hydrogen and carbon atoms, combines with oxygen in the air to produce carbon dioxide and water vapour as products of the combustion.
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 continues to burn, you can observe the smoke, which contains carbon dioxide. If you hold a cold surface near the flame, water droplets can condense on it, showing the production of water vapour.
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Heat, light, water vapour and carbon dioxide are created
When a candle is alight, it produces heat, light, water vapour, and carbon dioxide. The heat of the flame melts the wax near the wick, and this liquid wax is drawn up the wick through capillary action. The flame vaporises the liquid wax, turning it into a hot gas, and breaks down the hydrocarbons into molecules of hydrogen and carbon. These molecules are then drawn into the flame, where they react with oxygen from the air. This creates heat, light, water vapour, and carbon dioxide.
The blue area at the base of the flame is where the oxygen-rich hydrocarbon molecules vaporise and break apart into hydrogen and carbon atoms. The hydrogen separates first and reacts with oxygen to form water vapour. Some of the carbon burns here to form carbon dioxide. Above the blue zone is a small dark orange-brown section, where carbon continues to break down and form hardened carbon particles. As they rise, along with the water vapour and carbon dioxide, they are heated to around 1000 degrees Centigrade.
At the bottom of the yellow zone, the formation of carbon (soot) particles increases. As they rise, they heat up and ignite, emitting a full spectrum of visible light. The yellow portion of the spectrum is the most dominant, so the human eye perceives the flame as yellowish. Near the top of the flame's yellow region, the temperature reaches approximately 1200 degrees Centigrade, and the soot particles oxidise. The outer blue edge of the flame is the fourth zone, where the flame takes on its elongated or teardrop shape due to the convection current of upward-moving air.
The amount of gas produced by a candle is relatively small, and the gases mix into the room's air, becoming indistinguishable from other molecules. Over time, these molecules escape the room and disperse. While the levels of carbon dioxide and water vapour produced by candles are typically low, constant exposure to candle particles can contribute to indoor air pollution and lead to respiratory issues. Therefore, it is recommended to ensure proper ventilation when burning candles and use clean, white candles with fewer additives.
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The flame flickers or flares if there's too much or little air/fuel
When a candle is alight, the heat of the flame melts the wax near the wick. The liquid wax is drawn up the wick and the heat of the flame vaporizes it, breaking down the hydrocarbons into molecules of hydrogen and carbon. These molecules react with oxygen from the air to create heat, light, water vapour, and carbon dioxide.
The flame of a burning candle requires a delicate balance of air and fuel. If there is too much or too little of either, the flame will be affected. For example, if there is too much fuel, the flame may grow larger over time, eventually becoming a fire hazard. This can be mitigated by trimming the wick to limit the amount of fuel being burned. Conversely, if there is insufficient fuel, the flame may reduce in size and eventually go out. This can occur if the wick is clogged or if the fragrance oil in the wax contains non-combustible ingredients that accumulate in the melt pool.
Similarly, if there is too much air, the flame may flicker or flare, and unburned carbon particles (soot) will escape from the flame before they can fully combust. This can be caused by a draft, which can also cause the flame to go out. On the other hand, if there is too little air, the flame may struggle to stay alight due to insufficient oxygen for combustion.
The ideal flame size for smaller candles is between 1/2 to 1 inch, measured from the bottom of the flame arc to the tip. A flame that reaches up to 2 inches is typical for pillars and large taper candles. Any higher than that could be problematic and may indicate that the wick is too long or that there is too much wax being drawn up into the flame.
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Burning candles for too long can cause smoke and soot
Burning a candle is a simple way to add ambiance to a room, but it's important to follow some basic safety guidelines. One common mistake people make is burning candles for too long, which can lead to several issues. Firstly, leaving a candle burning for an extended period can cause carbon to build up on the wick, leading it to "mushroom". This happens when the candle consumes more wax than it can burn, causing the wick to become unstable and the flame to grow too large. As a result, the candle may start to smoke and release soot into the air and around the candle container.
To prevent this, it is generally recommended that candles are not burned for longer than four hours at a time and that they are allowed to cool for at least two hours before being relit. It's also important to always trim the wick to 1/4 inch before lighting the candle and to remove any debris from the wax pool, such as wick trimmings or matches. This helps to ensure the candle burns evenly and reduces the risk of flare-ups or small fires.
Another issue that can arise from burning candles for too long is the formation of a "memory ring". This occurs when a candle is not burned long enough to allow the wax to liquefy or melt from edge to edge. Once a "memory ring" forms, the candle will continue to tunnel, resulting in wasted wax. To avoid this, it is recommended that candles are burned for one hour for every inch in diameter of the candle size. For example, a 2-inch candle should be burned for two hours.
Additionally, burning a candle for too long can affect its performance and longevity. Highly fragrant candles, for example, have a lifespan of 6 to 12 months, depending on the scent. Burning these candles for extended periods can cause them to deteriorate in appearance and performance, so it is recommended to use and replace them frequently.
Finally, it's important to be mindful of the potential safety hazards associated with burning candles for too long. Aside from the increased risk of flare-ups or small fires, moving air from fans, open windows, or people walking by can disturb the flame, resulting in black marks on the glass or surrounding areas. Therefore, it is recommended to avoid burning candles near these sources of moving air. By following these guidelines, you can safely enjoy your candles and avoid the issues that can arise from burning them for too long.
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Frequently asked questions
The heat of the flame melts the wax near the wick, which is then drawn up the wick and evaporates. The liquid wax then breaks down into hydrogen and carbon atoms, which react with oxygen in the air to create heat, light, water vapour, and carbon dioxide.
The blue area is the hottest part of the flame, reaching temperatures of up to 1400° C (2552° F). It is where hydrocarbon molecules vaporise and break apart into hydrogen and carbon atoms.
If a candle flame gets too little or too much air or fuel, it can flicker and release unburned carbon particles (soot). This can also be caused by debris in the wax pool, or uneven burning due to a long or crooked wick.
A "memory ring" is created when a candle is not burned long enough for the wax to liquefy from edge to edge. Once a candle has a "memory ring", it will continue to tunnel for the rest of its life.
Constant exposure to candle particles can lead to cardiovascular and respiratory issues. While the amount of gas produced by a candle is small, it is recommended to ensure the room is well-ventilated to minimise exposure to airborne particles.
