A match is lit to light a candle. The following observations are made: (a) The candle burns. (b)

A match is lit to light a candle. The following observations...

Key Concepts

Physical Change

A physical change involves a transformation in the state or appearance of a substance without altering its chemical composition. Processes like melting and solidification are classic examples, as they only change the form (such as transitioning from solid to liquid) while leaving the molecular structure intact.

Chemical Change

A chemical change involves a transformation that produces new substances with different chemical properties. This kind of change occurs when existing bonds break and new ones form, such as during combustion reactions where substances like carbon (soot) are generated.

Phase Change

A phase change is a type of physical change where a material transitions between states, such as from solid to liquid or liquid to solid. These processes do not alter the material's chemical identity but only its physical state under different temperatures or pressures.

Combustion Reaction

A combustion reaction is a chemical change that occurs when a substance burns in the presence of oxygen, resulting in the formation of new products like carbon dioxide, water, and soot. This reaction is exothermic, releasing energy in the form of heat and light.

Transcript

00:01 We have the chemical versus physical changes, and more specifically, we're talking about candles today.

00:07 And the different stages that occur when you are lighting a candle.

00:11 So here in the first picture, it's when we are first initially lighting a candle.

00:16 The second one here is where there is a melting of the wax that is occurring.

00:20 This third picture here, we can see, maybe it may get a little bit bigger, actually, to see some of the wax has solidified onto the candle holder as we're a little bit all over the candle.

00:30 On the table and in this last picture it shows kind of a little bit of the black the carbon the soot that is being formed upon that after like lighting the candle of course and we want to go ahead and classify each of these four stages of the candle burning as either chemical or physical changes and here we have the definition of the chemical and physical change remember the chemical changes actually change the substance to something new that has different properties they're irreversible changes physical changes change only the appearance of the substance but not the chemical composition so those are reversible as in fact so let's look at this first one here let's go ahead and label these just kind of make it a little bit easier to see and identify it is going to be member step one step two this is going to be step three and lastly step four so step one is the initial lighting of the candle and then that itself is going to be a chemical change now the reason why it's a chemical change is because it actually goes again a chemical reaction to form other products like carbon dioxide so the actual lighting you are causing a chemical reaction to start occurring so that initial step is a chemical change.

01:45 It is irreversible you whatever is being given off cannot be converted back to the actual candle so that is chemical the second step of the candle burning and whatnot is the melting of our phase is where some of the wax is starting to melt from the heat and this is actually going to be a physical change so you're we're talking about the candle specifically um the candle uh essentially it will eventually when it gets cooler it will get it will that the parts that were melted can't get hard and so and once it gets hot again um it'll start to melt once again so this is a reversible process so it's going to be a physical change just like the third step where it is solidified where it's solidified you can go ahead and try to melt that once more and then you can try to solidify it again if you could get it to a place where it starts to harden once again so between the melting and you know making go liquid wax versus solid wax those are physical changes you are changing the appearance of the wax and those on step two and step three so those are physical changes no real chemical reaction is occurring on the wax itself in terms of it melting and then you and turning to wax of course and having it hardened...

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