What is fire?

1. What is fire?

2. How do candles burn?

3. The candle Flame Wick (absorbent cord, twine) Paraffin wax

4. The candle • A candle is a tool for slowly vaporizing and burning wax. When the wick is set on fire, the heat melts some of the wax at the top of the candle. The melted wax soaks the wick and becomes so hot that it turns to a gas. The gas burns brightly, giving off light. When you blow out a candle, the force of your breath pushes the heat of the flame away from the candle. The temperature of the wick cools until it is too low for the candle to burn.

5. How do things catch fire? • Fire is the result of a chemical reaction, called combustion. Typically, this chemical reaction is between oxygen in the atmosphere and some sort of fuel (wood or gasoline, for example). • Wood and gasoline don't catch on fire on their own just because they're surrounded by oxygen. For the combustion reaction to happen, the fuel needs to reach its ignition temperature. The ignition temperature of any material is the point at which it will catch fire For example, wood gets heated to a very high temperature. The heating can come from different sources - a lit match, focused light, friction, lightning or even something else burning nearby. When the wood reaches 150 degrees Celsius, the heat decomposes some of the cellulose material that makes up the wood. Some of the decomposed material is released as volatile gases. We know these gases as 'smoke'. When these volatile gases are hot enough (about 260 degrees Cfor wood), the compound molecules break apart, and the atoms recombine with the oxygen to form water, carbon dioxide and other products. In other words, they burn.

6. How do things catch fire? What sustains a fire is the fact that the chemical reactions in a fire generate a lot of new heat. The heat of the flame itself keeps the fuel at the ignition temperature, so it continues to burn as long as there is fuel and oxygen around it. The flame heats any surrounding fuel so it releases gases as well. When the flame ignites the gases, the fire spreads. While the gasous compounds burn, the rest of the material forms char, which is nearly pure carbon, and ash, The char is what you buy when you buy charcoal. Charcoal is wood that has been heated to remove nearly all of the volatile gases and leave behind the carbon. That is why a charcoal fire burns with no smoke.

7. What is the State of Matter of Fire or Flame? Is it a Liquid, Solid, or Gas? The ancient Greeks and alchemists thought that fire was an element. They also considered earth, air, and water to be elements. Fire is made up of many different substances For the most part, fire is a mixture of hot gases. Flames are the result of a chemical reaction, primarily between oxygen in air and a fuel, such as wood or propane. In addition to other products, the reaction produces carbon dioxide, steam, light, and heat. If the flame is hot enough, the gases are ionized and become yet another state of matter: plasma.

8. States of MatterSolids, Liquids, Gases & Plasma Solids A solid has a definite shape and volume. Examples of solids include ice (solid water), a bar of steel, and dry ice (solid carbon dioxide). Liquids A liquid has a definite volume, but takes the shape of its container. Examples of liquids include water and oil. Gases A gas has neither a definite volume nor a definite shape. Examples of gases are air, oxygen, and helium. Some introductory chemistry texts name solids, liquids, and gases as the three states of matter, but higher level texts recognize plasma as a fourth state of matter. Plasma Plasma has neither a definite volume nor a definite shape. Plasma often is seen in ionized gases. Plasma is distinct from a gas because it possesses unique properties. Free electrical charges (not bound to atoms or ions) cause plasma to be electrically conductive. Plasma may be formed by heating and ionizing a gas. Stars are made of plasma. Lightning is plasma. You can find plasma inside fluorescent lights and neon signs.

9. matches The chemicals that make up the match head have a relatively low ignition temperature—roughly 360 degrees F. Sliding the head across the rough surface produced a temperature at least this high. Once the match head ignited, combustion released even more heat. Because this heat was higher than the matchstick's ignition temperature, the fire is sustained. It then moved from the head to the cardboard stick.

10. Strike a Match To initiate and sustain combustion, three things are needed: fuel, oxygen, and heat. These three components make up what is known as the fire triangle. Each type of fuel has an ignition temperature, which is the threshold temperature at which that fuel can rapidly unite with oxygen. Above, two of the three components of the fire triangle are available. All that is needed to light the match is heat. Dragging the match across the rough surface will generate heat due to friction. If the match moves fast enough, friction will generate enough heat and the match will ignite.

11. Fireworks! • http://scifun.chem.wisc.edu/chemweek/fireworks/fireworks.htm

12. Fireworks! • The colors are produced by heating metal salts, such as calcium chloride or sodium nitrate, that emit characteristic colors. • The atoms of each element absorb energy and release it as light of specific colors. • The energy absorbed by an atom rearranges its electrons from their lowest-energy state, called the ground state, up to a higher-energy state, called an excited state. The excess energy of the excited state is emitted as light, • A common example of such material is sodium in table salt. If salt is sprinkled into a flame, an orange color appears. The colored flame is a result of electrons in sodium ions absorbing energy and moving up to higher energy levels and then falling back to their ground state, emitting specific amounts of energy that correspond to colors of light.