If you place a glass rod over a burning candle, the glass...

If you place a glass rod over a burning candle, the glass appears to turn black. What is happening to each of the following (physical change, chemical change, both, or neither) as the candle burns? Explain each answer.
a. the wax
b. the wick
c. the glass rod

Key Concepts

Soot Deposition

Soot deposition is the process by which tiny carbon particles, formed during incomplete combustion, are carried by hot gases and settle onto nearby surfaces. This is essentially a physical process where the deposition of these particles changes the appearance of the surface without altering the chemical structure of the glass or the soot itself.

Combustion

Combustion is a type of chemical reaction typically involving a fuel reacting with an oxidant, such as oxygen, to produce heat and light. This reaction often results in the formation of new molecules such as carbon dioxide and water, and can also produce byproducts like soot, which is a result of incomplete combustion.

Physical Change

A physical change involves a modification in the state, form, or appearance of a substance without changing its inherent chemical composition. Examples of physical changes include melting, freezing, and deposition, where the substance retains its original chemical identity despite undergoing observable transformations.

Chemical Change

A chemical change refers to a process where one or more substances are transformed into new substances with different chemical properties. This involves the breaking and forming of chemical bonds and is often accompanied by the release or absorption of energy in the form of heat, light, or sound.

Transcript

00:01 So you're holding a glass rod over burning.

00:04 Um, and you want to figure out what's happening to each of the components, right? so, physical change, chemical change.

00:14 Potentially both.

00:16 Um, so let's start with wax.

00:17 Right? so physical changes are defined by, um, most cases a phase changed, but, um, a lack of change in the chemical composition, right.

00:32 So wax melting.

00:34 Let's say so.

00:35 When you burn the candle, you get melted, right? so that is gonna be a physical change, because when you melt the wax, it goes from solid to liquid.

00:51 But if you cool it, it's just gonna become a solid again.

00:53 You could melt it so the wax is still wax.

00:57 So let's say that you heat the wax to a temperature, so this potentially might happen when you light a candle.

01:02 Let's say that you start burning the lax, right? so let's say that you are potentially undergoing some kind of a combustion reaction with the wax.

01:12 That would be a chemical change.

01:14 So potentially you burning wax when your wedding a candle.

01:18 11 candle burn.

01:20 May that may lead to both physical and chemical changes happening.

01:24 I would say the wax will melt before it burns.

01:27 But, um, i can't you can't say that both wouldn't happen.

01:31 The wick, on the other hand, you are physically lighting with fire with a match with a lighter.

01:38 Right? so the wick is his toast.

01:41 The wick is burning...

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