Understanding the Temperature of a Flame
During a combustion reaction, chemical bonds are broken and thermal energy (heat) is released. Fuel and oxygen are converted into carbon dioxide and water during combustion. Initially, the reaction requires energy to break bonds in the fuel and between oxygen atoms, but the amount of energy released when atoms bond together to form carbon dioxide and water is much greater.
The fuel + oxygen + energy + carbon dioxide + water + more energy
Energy is released both in the form of light and heat. There is visible evidence of this energy in the form of flames. Most flames are composed of hot gases. Like a stove burner, embers glow because they emit incandescent light, while flames emit light from ionized gases. Although firelight is a visible indication of combustion, thermal energy (heat) may also be invisible.
Why Fire Is Hot
Fire is hot because the stored energy in fuel is released suddenly. Compared to the energy released, much less energy is required to initiate the chemical reaction.
Key Takeaways: Why Is Fire Hot?
- It does not matter what fuel is used to ignite fire, it will always be hot.
- The net heat released by combustion exceeds the activation energy (ignition).
- In the process of breaking the chemical bond between oxygen molecules, energy is absorbed, but the process of forming the chemical bonds between the products (carbon dioxide and water) releases much more energy.
How Hot Is Fire?
The amount of thermal energy released by fire depends on several factors, including the chemical composition of the fuel, oxygen availability, and the portion of the flame being measured. It is possible for a wood fire to exceed 1100° Celsius (2012° Fahrenheit), but different types of wood burn at different temperatures. As an example, pine produces twice as much heat as fir or willow, and dry wood burns hotter than green wood. It burns at a similar temperature in air (1980° Celsius), but at a much hotter temperature in oxygen (2820° Celsius). There are other fuels that burn hotter than wood, such as acetylene in oxygen (3100° Celsius).
Fire color is a rough indication of its temperature. Red fire reaches 600-800° Celsius (11112-1800° Fahrenheit), orange-yellow fire reaches 1100° Celsius (2012° Fahrenheit), and white fire reaches 1300-1500° Celsius (2400-2700° Fahrenheit). The hottest flame is blue, with a temperature ranging from 1400-1650° Celsius (2600-3000° Fahrenheit). Bunsen burners have blue gas flames that are much hotter than wax candles.
Hottest Part of a Flame
If the flame burns that hot, the point of maximum combustion is the blue portion of the flame. However, most students performing science experiments are instructed to use the top of the flame. What’s the reason? Heat rises, so the top of the flame’s cone is a good collection point for energy. Furthermore, the cone of the flame has a fairly consistent temperature. A flame’s brightest portion can also be used to determine the most heated region.
Fun Fact: Hottest and Coolest Flames
At 4990° Celsius, the hottest flame ever produced was produced. Ozone was used as the oxidizer and dicyanoacetylene as the fuel for this fire. It is also possible to make a cool fire. By regulating the air-fuel mixture, a flame around 120° Celsius can be created. This type of fire, however, is difficult to maintain since a cool flame is barely over the boiling point of water.
Fun Fire Projects
Perform interesting science projects to learn more about fire and flames. Learn how metal salts affect flame color by making green fires. Are you looking for a truly exciting project? Firebreathing is something you should try.