Why is there both a physical and a chemical change when lighting a candle?

Physical Changes: Candles emit heat when burned; The paraffin wax melts when heated and its state changes.

Chemical change: Paraffin wax burns with heat, and wax burns to produce water'Carbon dioxide.

Therefore, there are two processes: melting by heat and forming other substances.

2.Wax combustion to produce water and carbon dioxide is a chemical reaction.

Wax combustion is first heated and melted, and when the combustible temperature is reached, the chemical reaction is carried out to produce other substances During the candle burning process, the wax in the candle will react with the air to produce carbon dioxide and water. So. When lighting a candle, have you ever noticed that when you put a lit match or lighter close to the candle, the wax near the wick will partially melt and melt?

The contemptible person just graduated from high school Shame ashamed Shame Shame Shame T

If you are not satisfied, forgive me!

The melting of a candle by heat is a physical change; Candles are burned to produce carbon dioxide and water, which are chemical changes. When the candle is heated, it first changes from a solid state to a liquid state, which belongs to the melting process of the candle, and there is no new material generation, which belongs to physical change; Candles are burned to produce carbon dioxide and water, and new substances are formed, which is a chemical change.

Physical Changes:1Definition: No change in the formation of other substances.

2.Example: A light bulb glows, and ice melts into water; Water evaporates into water vapor; Iodine, sublimation of dry ice, volatilization of gasoline, melting of candles, etc., are all physical changes.

Chemical changes:1Definition: A change in a substance that generates a change in other substances.

2.Examples: Sticks of wood burning, iron rusting, food rotting.

3.Phenomenon: Chemical changes are often accompanied by some reaction phenomena while generating new substances, which are manifested as color changes, gas releases, precipitation, etc., chemical changes not only generate other substances, but also are accompanied by energy changes, which are often manifested as endothermy, exothermics, luminescence, etc.

A chemical change is a change in the elemental composition of a substance.

For example, the main gas produced by combustion is carbon dioxide.

Physical change refers to a change in the state of matter.

Such as the solid state becomes gaseous, etc.

The candle then emits a lot of heat.

Causes nearby candles to melt

The following phenomena can be clearly seen.

It is a solid candle that changes from a solid state to a liquid state, while the temperature of the other parts cools down, and then it becomes a solid candle.

Candle burning is a chemical change.

When a candle is burned, the product of combustion is carbon dioxide.

and water. The combustion phenomenon in the oxygen cylinder is that the flame is bright and emits white light, emitting heat, and there is a mist of water on the wall of the cylinder. When the candle is lit, the initial flame becomes smaller and smaller, and the flame is divided into three layers (outer flame, inner flame, flame center). The flame core is mainly candle steam, the lowest temperature, paraffin.

Insufficient combustion within the flame and the temperature is higher than the flame center.

Because there are some carbon particles, the outer flame is in full contact with the air, the flame is the brightest, the combustion is sufficient, and the temperature is the highest. Therefore, when the matchstick is quickly laid flat in the flame, it is removed after about 1 second, and the part of the matchstick that touches the outer flame turns black first.

At the moment of blowing out the candle, a puff of white smoke can be seen, which can be re-lit by a burning match, thus proving that the white smoke is a small solid particle produced by the condensation of paraffin vapor.

Candles, a tool for daily lighting, are mainly made of paraffin wax, and in ancient times, were usually made from animal fat. Combustible glows. In addition, candles are very versatile:

It is also used in birthday banquets, religious festivals, collective mourning, ceremonies and other activities. In literary and artistic works, candles have symbolic meanings of sacrifice and dedication.

In modern times, it is believed that candles originated from torches in primitive times, when primitive people applied things such as fat or wax to the bark or wood chips, tied them together, and made torches for lighting. There is also a legend that in the pre-Qin antiquity, someone put mugwort.

It was tied into a bunch with reeds, dipped in some grease and lit for lighting, and later a hollow reed was wrapped in cloth and filled with beeswax.

Ignite. The main raw material of candles is paraffin wax (ch) Paraffin wax is prepared from the wax-containing fraction of petroleum by cold pressing or solvent dewaxing, and is several high-grade alkanes.

mixture. Mainly n-docadene (C22H46) and n-octadecane (C28H58), which contain carbon elements.

Approximately 85%, containing hydrogen.

About 14%. The added excipients are white oil, stearic acid, and polyethylene.

Flavors, etc., among which stearic acid (C17H35COOH) is mainly used to improve softness, depending on what kind of candle is produced.

It is easy to melt, the density is less than that of water, and it is difficult to dissolve in water. It melts into a liquid state when heated, colorless, transparent and slightly volatile when heated, and can smell the unique odor of paraffin. When cold, it solidifies into a white solid form with a slight special odor.

When the candle is heated, it first changes from a solid state to a liquid state, which belongs to the melting process of the candle, and there is no new material generation, which belongs to physical change; Candles are burned to produce carbon dioxide and water, and when new substances are generated, they are hungry, which is a chemical change

Answer: The melting of candles by heat is a physical change; Sun Song candles burn their limbs into carbon dioxide and water, which is a chemical change

Categories: Science & Engineering.

Problem description: Why is it said that when lighting a candle, there is a physical change in the orange chain before and a change in the posterior evolutionary line?

Analysis: Because when the candle is lit, the candle melts when it is heated, which is a physical change.

The composition of the candle is paraffin, which is burned in oxygen to produce carbon dioxide and water, which is a chemical change.

When the candle is heated, it first changes from a solid state to a liquid limb belt, which belongs to the melting process of the candle, and there is no new material generation, which belongs to the physical change; Candles are burned to produce carbon dioxide and water, and new substances are generated, which belongs to the chemical Sun Song change

Therefore, the answer is: the heating and melting of candles is a physical change; Candles are burned to produce carbon dioxide and water, which are chemical changes.

Candle burning has both physical and chemical changes, melting is a physical change, and burning is a chemical change. In general, it is a chemical change, because a new substance is generated, and the chemical change must be accompanied by a physical change.

Combustion is a kind of exothermic and luminescent chemical reaction, and its reaction process is extremely complex, the chain reaction of free radicals is the essence of the combustion reaction, and light and heat are the physical phenomena that occur during combustion.

Combustibles undergo a rapid exothermic and luminescent oxidation reaction with oxygen or air and appear in the form of a flame. The combustion of coal, oil, and natural gas is the main thermal energy power of all sectors of the national economy. The rapid increase in energy demand and the rapid development of aerospace technology in modern times have promoted the combination of fluid mechanics, chemical reaction kinetics, and heat and mass transfer, which has led to the rapid development of combustion science. On the other hand, the development of fire prevention technology for the purpose of eliminating combustion has also promoted the research of combustion theory.

There are physical and chemical changes.

The composition of the candle is paraffin.

When burning, the paraffin solid melts and then vaporizes to form paraffin vapor, which is a physical change. (The part near the fire does not burn and becomes liquid, which is also a physical change.) ）

The paraffin vapor and oxygen undergo a combustion chemical reaction, which is a chemical change here.

Candle burning is a chemical change in which hydrocarbons are burned to produce CO2 and water (incomplete combustion also produces carbon).

Chemical changes, paraffin wax violently oxidizes and emits light and heat, mainly to produce water and carbon dioxide, and incomplete combustion to produce carbon particles and carbon monoxide.

Burning alone is a chemical change, but the melting of a candle is a physical change, and the candle becomes a solid particle.

It is a chemical reaction because there is a change in the substance and there is a new substance that is produced. All combustion reactions are chemical reactions, hope.