Grade 9 Chemistry, Lesson 3 - Physical and Chemical Properties and Changes

Summary

This chemistry lesson explores the distinction between physical and chemical properties and changes. Physical properties, such as state of matter, color, and density, can be measured without altering a substance. Chemical properties, however, require a reaction to be observed. The video clarifies this by contrasting physical changes, like cutting bread or turning on a light, with chemical changes, such as baking bread or frying an egg, which result in new substances. It also discusses how to identify chemical changes through color changes, heat production, and irreversibility.

Takeaways

• 🧪 Physical properties are characteristics of substances that can be measured without changing the substance's identity, such as state of matter, color, density, and hardness.
• 🔨 Hardness is the resistance of a solid to being scratched or dented, as illustrated by the scratches on a canoe from rocks.
• 🛠 Malleability refers to how easily a substance can be hammered or bent into different shapes, with metals and Play-Doh being examples of malleable substances.
• 🧵 Ductility is the ability of a substance to be pulled into wires without breaking, as demonstrated by stretching aluminum.
• 💧 Solubility is a physical property that describes a substance's ability to dissolve in a solvent, like salt dissolving in water.
• 🍯 Viscosity is a measure of a liquid's resistance to flow, with honey being an example of a highly viscous substance.
• 🔥 Chemical properties describe a substance's potential to react chemically with other substances to form new compounds, and they can only be observed through chemical reactions.
• 🔥 Combustibility and flammability are chemical properties that indicate a substance's ability to react quickly with oxygen, producing heat and light, such as catching on fire.
• 🌡 Acidic or basic properties are also chemical properties that define how a substance reacts with other chemicals.
• 🥚 Chemical changes involve the creation of a new substance, such as the reaction of hydrogen and oxygen to form water (H2O).
• 🧊 Physical changes do not result in the creation of a new substance, but may involve a change in state, like water turning into ice.

Q & A

What are physical properties?

Physical properties are characteristics of substances that can be measured or observed without changing the composition of the substance. Examples include state of matter, boiling and melting points, color, luster, density, hardness, malleability, ductility, and solubility.

What is the difference between hardness and malleability?

Hardness is the resistance of a solid to being scratched or dented, while malleability describes how easily a substance can be hammered or bent into different shapes.

Can you give an example of a physical property that demonstrates ductility?

An example of ductility is a tube of aluminum, which can be stretched out into a longer, thinner version without snapping.

What is solubility in the context of physical properties?

Solubility is the ability of a substance to dissolve in a solvent, such as salt dissolving in water.

How does viscosity relate to the flow of a liquid?

Viscosity of a substance describes how quickly it flows in its liquid form. A higher viscosity indicates a slower flow, like honey pouring slowly over a plate.

What are chemical properties?

Chemical properties describe the ability of a substance to chemically react with another substance to produce a new chemical. They can only be observed through a chemical reaction.

What are some examples of chemical properties?

Examples of chemical properties include combustibility (ability to react with oxygen and produce heat and light) and acidity or basicity, which describe reactions with other chemicals.

How can you distinguish between a chemical change and a physical change?

A chemical change involves the creation of a new substance, while a physical change involves a change in state or appearance without the formation of a new substance.

What are some indicators that a chemical change has occurred?

Indicators of a chemical change include the appearance of a new color, the release of heat or light, the formation of gas bubbles, the creation of a precipitate when two liquids are mixed, and the difficulty of reversing the change.

Can you provide an example of a chemical change from the script?

An example of a chemical change from the script is baking a loaf of bread, which is hard to reverse and involves a color change.

What is the difference between turning on a light bulb and frying an egg in terms of physical and chemical changes?

Turning on a light bulb is a physical change because it can be easily reversed and does not involve the creation of a new substance, while frying an egg is a chemical change due to the color change and the difficulty of reversing the process.

Outlines

00:00

🔬 Physical and Chemical Properties and Changes

In this segment, Mr. Lehan introduces the concepts of physical and chemical properties and changes in the context of grade N chemistry. Physical properties are measurable characteristics like state of matter, boiling and melting points, color, luster, density, hardness, malleability, ductility, solubility, and viscosity. These properties can be observed without changing the substance's chemical identity. Chemical properties, on the other hand, describe how substances react with others to form new substances, and they can only be observed through chemical reactions. Examples include combustibility, acidity, and basicity. The distinction between physical and chemical changes is also discussed, with chemical changes involving the formation of new substances, often indicated by color change, heat or light emission, gas formation, or precipitate formation, and being difficult to reverse.

05:01

🔍 Distinguishing Between Physical and Chemical Changes

This paragraph delves into differentiating between physical and chemical changes through various examples. Baking bread is identified as a chemical change due to its irreversibility and color change, while cutting bread is a physical change as it only alters the shape without creating new substances. Putting peanut butter on bread and mixing red and yellow paint to make orange are also physical changes, as they involve combining existing substances without altering their molecular structures. Setting bread on fire and frying an egg are classified as chemical changes due to the production of light and heat, color change, and the difficulty of reversing the process. The segment also touches on the tricky case of turning on a light bulb, which, despite producing light and heat, is a physical change because it is easily reversible.

Keywords

💡Physical properties

Physical properties are the characteristics of a substance that can be observed or measured without changing the substance's chemical identity. They are central to the video's theme of distinguishing between physical and chemical changes. Examples from the script include the state of matter at room temperature, boiling and melting points, color, luster, density, hardness, malleability, ductility, solubility, and viscosity. These properties help to classify and understand substances without altering their composition.

💡Chemical properties

Chemical properties describe the potential reactions of a substance with other substances, which can only be observed through chemical reactions that result in new substances. They are key to the video's discussion of chemical changes. The script mentions combustibility, flammability, acidity, and basicity as examples of chemical properties, which determine how substances interact at a molecular level to form new compounds.

💡Chemical changes

A chemical change is a process where one or more substances are transformed into new substances with different properties. The video emphasizes that chemical changes are characterized by the formation of new substances. Examples provided include baking bread, which results in a new substance with a color change, and frying an egg, which is irreversible and involves a color change, indicating new chemical substances are formed.

💡Physical changes

Physical changes involve alterations in the form or state of a substance without changing its chemical composition. The video script uses the example of cutting a slice of bread to illustrate a physical change, where the shape is altered but the chemical makeup remains the same. Turning on a light bulb, despite producing light and heat, is also considered a physical change because it is easily reversible and no new substances are created.

💡Hardness

Hardness is a physical property that refers to the resistance of a material to being scratched or dented. The video script relates this to the example of a canoe with scratches, indicating that the canoe's material is less hard than the rocks it encountered. Hardness is an important property in material science and engineering, affecting the durability and practical applications of substances.

💡Malleability

Malleability is the ability of a material to be hammered or bent into different shapes without breaking. The video script illustrates this with a hot piece of metal being hammered out. This property is significant in metalworking and is a key characteristic of metals, which are often used in various forms due to their malleability.

💡Ductility

Ductility is the property of a material to be stretched into a wire without breaking. The video uses the example of pulling on a tube of aluminum to demonstrate this property. Ductile materials like metals are valuable in industries where the ability to draw materials into thin wires or sheets is necessary.

💡Solubility

Solubility is a physical property that describes a substance's ability to dissolve in a solvent. The script provides the example of salt dissolving in water, indicating that salt is soluble. Understanding solubility is crucial in chemistry and various industries, such as pharmaceuticals and food processing, where substances are mixed in solutions.

💡Viscosity

Viscosity is the measure of a liquid's resistance to flow. The video script uses the example of honey being poured, which folds over on itself due to its high viscosity. Viscosity is important in various applications, including lubrication, paint formulation, and the behavior of fluids in different environments.

💡Combustibility

Combustibility, also known as flammability, is a chemical property that describes a substance's ability to catch fire and burn rapidly when exposed to oxygen. The video script mentions this in the context of chemical properties, indicating that a combustible substance will undergo a chemical reaction with oxygen, producing heat and light.

💡Acidic and Basic

Acidity and basicity are chemical properties that describe how substances react with other chemicals. The video script explains that these properties are important in chemical reactions, where acids and bases can neutralize each other or react with other substances to form new compounds. Understanding the pH scale and the properties of acids and bases is fundamental in chemistry.

Highlights

Introduction to physical and chemical properties and changes in grade N chemistry.

Physical properties are characteristics of substances that can be measured without changing the substance.

Examples of physical properties include state of matter, boiling and melting points, color, luster, density, hardness, malleability, ductility, and solubility.

Hardness is the resistance of a solid to being scratched or dented, illustrated with a canoe with scratches.

Malleability is the ability of a substance to be hammered or bent into different shapes, as shown with hot metal being hammered.

Ductility is the ability of a substance to be pulled into wires without snapping, using aluminum as an example.

Solubility is the ability of a substance to dissolve in a solvent, demonstrated with salt dissolving in water.

Viscosity describes how quickly a liquid flows, using honey pouring as an example of a viscous substance.

Chemical properties describe a substance's ability to chemically react with another to produce a new chemical.

Chemical properties require a chemical reaction to be observed, such as combustibility or acidity.

Chemical changes involve the creation of a new chemical substance, like hydrogen and oxygen reacting to form water.

Physical changes do not create new substances but involve changes in state or form, such as water freezing.

Clues of a chemical change include new color, heat or light production, gas bubbles, precipitate formation, and difficulty in reversing the change.

Baking bread is a chemical change due to its irreversibility and color change.

Cutting bread is a physical change as it only alters the shape without creating new substances.

Putting peanut butter on bread is a physical change with no new molecules being created.

Setting bread on fire is a chemical change characterized by light and heat production and color change.

Mixing red and yellow paint to make orange is a physical change despite the color change.

Turning on a light bulb is a physical change, not a chemical change, despite producing light and heat.

Frying an egg is a chemical change due to color change and irreversibility, characteristic of cooking.

Upcoming video on the history of atomic theory to be released.

Transcripts

all right welcome to Mr lehan teaches

you stuff this is grade n chemistry

lesson three physical and chemical

properties and

changes so physical properties describe

the characteristics of substances that

we can measure um and I'm just going to

go through several examples of physical

properties now so you get an idea of

what they are and if they require a

little bit more explanation I'll give a

quick definition of what they are so the

state of matter at room temperature is a

physical property so whether something's

a solid a liquid or a

gas other physical properties include

the boiling and melting points the color

the shininess or the luster and the

density of an object these are all

physical

properties another one is hardness and

hardness is the resistance of a solid to

being scratched or

dented um this is a picture here of my

canoe it's got a bunch of scratches on

the bottom and that's because my canoe

was not as hard as the rocks that I ran

into

so that's what hardness is uh

malleability describes how easily a

substance can be hammered or bent into

different

shapes so here we have a picture of a

piece of very hot metal being hammered

out uh most metals are fairly malleable

other things that would be malleable

would be uh Playdoh you can very easily

Hammer Play-Doh into different

shapes ductility that might be another

one you're not too familiar with this is

how easily a substance can be pulled out

into wires without snapping so if we

have a little you know tube of aluminum

or something here when you pull on

either end it'll get stretched out

without snapping into a longer thinner

version of itself that's

ductility solubility is the ability of a

substance to dissolve in a solvent so

for instance salt is dissolving in water

here so the salt is soluble in the water

that's a physical

property viscosity of a substance

describes how quickly it flows in its

liquid form so here we have a picture of

some honey being poured onto a plate and

you can see that the honey is sort of

folding over on itself and that's

because it's very viscous so it flows

very

slowly all right now we're going to look

at chemical properties so chemical

properties describe the ability of a

substance to chemically react with

another substance to produce a new

chemical so for chemical properties it's

not something where you can measure it

without reacting it with something

to see a chemical property you have to

see a chemical reaction take

place so chemical properties can only be

seen when a chemical reaction happens

you can't just look at something and say

wow that looks basic or that looks

acidic there's going to have to be some

sort of chemical reaction for you to you

to

tell so some examples of chemical

properties uh if a substance is

combustible or flammable that means it

will react quickly with oxygen and

produce heat light it'll catch on

fire uh if a substance is acidic or

basic that also describes how it reacts

with other chemicals so that's a

chemical

property okay so now we're going to look

at chemical and physical changes so not

properties but changes uh when a new

chemical substance is created it is a

chemical change so for example if we

have two hydrogen react with one oxygen

to make H2O or water that's going to be

a chemical change because a new

substance a new chemical substance the

water has been

created if on the other hand a chemical

is not changed right the chemicals don't

change there's nothing new it's a

physical change so if we have liquid

water turning into solid water or ice

this is a physical change things did

change it changeed State uh but the

chemicals are all the same so it's not a

chemical change

so here are several clues that a new

chemical has been

created a new color

appears heat or light are given off

bubbles of gas are

formed a solid material called a

precipitate appears when two liquids are

mixed and the change is difficult to

reverse so if you see any or all of

those it's usually a good clue that a

chemical reaction has taken place a

chemical change has taken

place all right so now we're going to go

through several different scenarios and

decide whether they are physical or

chemical changes so first off baking a

loaf of bread is this physical or

chemical this one's chemical it's very

hard to reverse you can't revert the

bread back into

dough uh and also a there's also a color

change right it's uh darker brown when

it's

baked what about cutting a slice of

bread this one is physical so although

it's hard to reverse you can't

unsliced uh the chemicals that you end

up with at the end are the same

chemicals that you started with right

nothing new has been created we've just

change the shape of the

bread putting peanut butter on

bread uh well this one the color changes

I guess cuz there's peanut butter on

it but you're still starting off with

bread and peanut butter and you end up

with bread and peanut butter so there's

really no change here there's no new

mole molecules being

created so this one is a physical

change what about setting the bread on

fire so we're producing light and heat

uh there will be a color change in the

bread it's getting sort of

blackened this is a chemical change you

will not be able to unfire this

bread mixing red and yellow paint to get

orange so here we definitely have a

color change and that was one of our one

of our clues that a chemical change has

happened but in this case this is a

physical change so we're really just

mixing all the little particles of paint

together to make an orange color but the

molecules that make up the paint have

not really changed they're all still the

same paint molecules if you

will all right turning on a light bulb

uh this one's a little tricky as well

because it produces light and heat which

is another one of our clues that a

chemical change has taken place but this

is very easy to reverse you just turn

the light switch back off and it goes

off so this is not a chemical change

this is just a physical

change and frying an egg this is our

last example frying an egg it definitely

changes color it's very difficult to

reverse basic well you can't reverse it

you can't unfry an egg

uh basically anytime you cook anything

or you bake

anything you are making a chemical

change so frying an egg is a chemical

change so that's it for this video uh

tune in for next video the history of

atomic theory