Are you looking to classify if a change is physical or chemical? Or you might be
wondering what is physical change? And what is chemical change?
Well, we're gonna answer all of these in this video.
Hi I'm Dr. K and welcome to ChemSimplified.
Let's jump straight in with the definitions of physical change.
It's a change that goes from one form to the other. It doesn't involve any change to
the chemical identity, meaning its chemical composition, so, it's still the
same substance after the change. So the effect that we see is only on the physical
properties and generally that change is easily reversible. So let me use an
example to illustrate physical change. Melting of ice. So let's think of ice.
Before melting it's solid H2O. After melting its liquid H2O. In terms of its
physical properties it has changed from solid state to liquid state, but in terms
of its chemical identity or the chemical property, there was no change to it.
It was H2O before melting it's still H2O after melting. So there's no change in
its chemical identity, meaning its still the same substance. The only change that
we notice is the effect on its physical properties, changing from solid state to liquid state.
Also, we can easily reverse this process by simply taking the melted
ice which is the water, place it in the freezer and it'll freeze again to become ice.
So, that basically illustrate physical change. Now we move on to chemical change.
Chemical change is a little bit different from physical change.
It's a change that's accompanied by a change in its chemical identity.
Meaning before and after the change, it is not the same substance. It forms new
substance and the effect that we see is going to be on both physical and
chemical properties, and usually it's very difficult to reverse the change.
So let me use an example burning paper. So if you imagine before burning the paper,
so you have a piece of paper. After you light it up, it burns and it burns into ashes.
So before burning it was a piece of
paper, solid. And after burning it becomes smaller
piece of paper, so there's a change that we observe in its physical properties.
In terms of its chemical properties, it changes its identity entirely.
It was paper before burning and then after that it became ash after burning.
Ash is not paper. It's a new substance. Also I can't reverse the change meaning I can't turn
the ash back into paper, so that basically Illustrated chemical change.
Let's go through some of the things I did this morning and classify them as
physical or chemical change. So the first thing I did this morning after waking up
was brushing my teeth. Now my toothpaste has fluoride ion in it so when I brush
my teeth the fluoride ion in the toothpaste changed the chemistry of my
teeth and what that did was it strengthened my teeth and helped prevent
future cavities from forming. So technically speaking that forms a new
substance on my teeth. Also that process is not reversible so
brushing teeth is a chemical change. After brushing my teeth, I hit the shower.
Since it was a hot shower, steam started forming. So what happens when hot water changed to steam?
Well there's an obvious change in its physical properties from
liquid state to gas state. However the chemical identity is still
the same. It's still H2O. So steam forming in the shower is a physical change.
After shower I head down for breakfast. So I pulled out an apple and washed it.
Since after washing the apple it didn't change to another fruit, it's therefore still
the same substance. So washing apple is a physical change.
same thing goes to cutting the apple. It only changed in size and its still apple,
so cutting apple is a physical change.
Then I decided to fry an egg because apple is just not enough.
So the heat from the pan causes the structure of the protein in the egg
to change permanently. That process is actually called protein denaturing.
Since this change is not reversible and the protein structure of my egg has changed permanently,
so frying an egg is a chemical change. Now I don't know
about you but my morning is not complete without coffee.
So I grinded some coffee beans. Grinding coffee beans only involved changing in its appearance.
Meaning it changed from whole beans to coffee grounds.
Since after grinding it's still the same substance which is coffee,
it's therefore physical change. After grinding the beans I brewed a cup of coffee.
So what happened was there was a transfer of taste and smell from the
coffee grounds to the hot water through an extraction which is a chemical reaction.
So that means my water was no longer just water. It became the elixir of life,
which is coffee. So brewing coffee is a chemical change
While taking a sip of coffee, well, I accidentally spilled my coffee on the
table, so I got a piece of paper towel from the kitchen. Tearing a paper towel
from its holder only changed its appearance from a roll of paper towel to
a piece of paper towel. It's still the same people towel so that means,
tearing paper towel is a physical change. Then I used that piece of paper towel to wipe
the coffee that I spilled. So after wiping coffee was absorbed onto the paper towel.
But the chemical identities of both my coffee and my paper towel remained the same.
Paper towel is still paper towel and the coffee is still coffee.
It's just absorbed onto the paper towel. I can easily reverse this process.
What I can do is I take my piece of paper towel that has coffee on it, soak it in water,
take it out and let it dry. So I'll get back my paper towel and my coffee is
left in that water, right? But of course I wouldn't drink that coffee anymore.
But since it's reversible and the substances remained the same, therefore
it's a physical change. Unfortunately, after breakfast I had to wash my dishes.
When I washed dishes, a chemical reaction occurred between the detergent and the
mess on the dishes. So that means the substance before and after washing are
no longer the same. The dish detergent is no longer the same. The chemical makeup
of the mess on my plate has changed as well.
So washing dishes is a chemical change.
Just to recap. Here's what we have classified
from what I've done this morning before recording this video.
Like I've mentioned before. When classifying change, it's to ask whether a new substance was formed.
If yes, then it's a chemical change. If no, then is a physical change.
Hope you find this video helpful. Do subscribe and check out my other videos.
For more practice questions on classifying physical and chemical change,
head over to ChemSimplified.com. I'll post a blog link below.
Thanks for watching and I'll see you in the next video.
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