Physical and Chemical Changes

Physical and Chemical Properties

Everything around us has physical and chemical properties.

Physical Properties

• Characteristics you can observe without changing the substance into something new.– Use your senses to describe– state of matter– measurement

• Use your senses… How does it look, smell, sound, feel, taste (don’t taste it unless the teacher says it’s ok)

• What state of matter is it? (solid, liquid, or gas)

• Measure it….mass, weight, volume, length, width, height, density, temperature, magnetic?

Physical Properties

• List as many physical properties as you can

Color

Temperature

Feel

Smell

State

Weight

Length

Density

Chemical Properties

• Will it burn, explode, react with other elements?

• Characteristics that you can only observe by changing the substance into something new.– You can’t always tell chemical properties just by

looking

Chemical Properties

• List as many chemical properties as you can

Will it burn

Will it explode

Can it react with other things

Physical and Chemical Changes

Matter around us can undergo changes.

Physical Changes

Chemical Changes

Physical Change

• A change in which the form or appearance of matter changes but not its composition– Change of state– Change of shape– Dissolving

Physical Changeschanging state

melting – solid to liquid condensation – gas to liquid

freezing – liquid to solid sublimation – solid to gas

vaporization – liquid to gas deposition – gas to solid

Changes in States

Physical Changeschange of shape

Matter can change shape

cutting

tearing

grinding

crumpling

bending

Physical Changesdissolving

When you mix or dissolve one thing into another, it is a physical change

Chemical Change

• A change in which the composition of matter changes and new substances are formed– It cannot easily be turned back into the original

substance

Chemical Change

• Signs that a chemical change may have taken place– Color change– Absorption or release of energy– Odor– Formation of gases or solids– Can’t be reversed

Signs of chemical changes• The best sign of a chemical change is that at

the end-you have a new substance!• Other common signs:

Color changeColor change

More signs of a chemical changeTakes energy or releases energy (cooking,

burning, produced light, electricity, fireworks)Before- mixing all of the ingredients, I could get all of the pieces back, so stirring together is a physical change

Before- mixing all of the ingredients, I could get all of the pieces back, so stirring together is a physical change

After I put the batter in the oven, the energy changes the make-up of the matter, I can not get batter back!

After I put the batter in the oven, the energy changes the make-up of the matter, I can not get batter back!

Releasing energy

Before: nothing in the sky (this was difficult to make. Before: nothing in the sky (this was difficult to make.

And after- fireworks!!!! Release energy as heat and light

And after- fireworks!!!! Release energy as heat and light

More signs of a Chemical Change

Change in smell or odor

Yummy milk- fresh from the cow (or super market)Yummy milk- fresh from the cow (or super market)

Rotten milk- I hope you never smell this!Rotten milk- I hope you never smell this!

Last sign of a chemical change• Making a gas or a solid without the use

of energy

Ammonium carbonate precipitates white SrCO3. Sr2+

(aq) + CO32-(aq) <==> SrCO3(s)

Ammonium carbonate precipitates white SrCO3. Sr2+

(aq) + CO32-(aq) <==> SrCO3(s)

Reversible

Q:What does it mean for a change to be reversible?

A:It can be put back - From Mirriam-Webster dictionary: capable of

going through a series of actions (as changes) either backward or forward <a reversible chemical reaction>

Is the change reversible?

• Folding paper?• Tearing your shirt? • Cutting your hair?• Eating an apple? • Burning some wood? • Cooking chicken?

Chemical ChangesIron + oxygen and water = rust

silver + oxygen and water = tarnish

Chemical Changes

Burned wood

Cooked food

Chemical ChangesLeaves turning in fall

Spoiled food

Chemical ChangesLightning bug

Antacid tablet

Physical or Chemical

Copper jewelry

Statue of Liberty

orange Orange juice Orange cake

copper

Physical Chemical

Physical Chemical

Law of Conservation of MassThe total mass of matter before and after

a physical or chemical change is the same.

Matter cannot be created or destroyed

The particles inside the matter rearrange to form new substances

Law of Conservation of Mass

Even though it appears that part of the candle disappears, it is just turned into a gas.– proven by Antoine Lavoisier

The Law of Conservation of MassThe law states that the total mass of the

matter is the same before as after any physical or chemical change.

Does that surprise you?That means everything that is here now- all of the matter- has always been here . This is all of the matter we have- in our universe

Does that surprise you?That means everything that is here now- all of the matter- has always been here . This is all of the matter we have- in our universe

ActivityLets practice using these words:

Procedure

1.Draw and label the physical properties of your piece of matter

2.Label any of the parts of your matter that have a chemical property

3.Make the matter change (wait for us)

4.Describe all physical and chemical changes (draw the after and label)