changes in matter

signs of chemical change

How can you tell whether a chemical change has occurred? Often, there are clues. Several are demonstrated in Figures 3.17 and 3.18 and in the video below. MEDIA Click image to the left or use the URL below. URL: To decide whether a chemical change has occurred, look for these signs: Gas bubbles are released. (Example: Baking soda and vinegar mix and produce bubbles.) Something changes color. (Example: Leaves turn from green to other colors.) An odor is produced. (Example: Logs burn and smell smoky.) A solid comes out of a solution. (Example: Eggs cook and a white solid comes out of the clear liquid part of the egg.)

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reversing chemical changes

Because chemical changes produce new substances, they often cannot be undone. For example, you cant change a fried egg back to a raw egg. Some chemical changes can be reversed, but only by other chemical changes. For example, to undo the tarnish on copper pennies, you can place them in vinegar. The acid in the vinegar reacts with the tarnish. This is a chemical change that makes the pennies bright and shiny again. You can try this yourself at home to see how well it works.

conservation of mass

If you build a campfire, like the one in Figure 3.19, you start with a large stack of sticks and logs. As the fire burns, the stack slowly shrinks. By the end of the evening, all thats left is a small pile of ashes. What happened to the matter that you started with? Was it destroyed by the flames? It may seem that way, but in fact, the same amount of matter still exists. The wood changed not only to ashes but also to carbon dioxide, water vapor, and other gases. The gases floated off into the air, leaving behind just the ashes. Assume you had measured the mass of the wood before you burned it. Assume you had also trapped the gases released by the burning wood and measured their mass and the mass of the ashes. What would you find? The ashes and gases combined have the same mass as the wood you started with. This example illustrates the law of conservation of mass. The law states that matter cannot be created or destroyed. Even when matter goes through physical or chemical changes, the total mass of matter always remains the same. (In the chapter Nuclear Chemistry, you will learn about nuclear reactions, in which mass is converted into energy. But other than that, the law of conservation of mass holds.) For a fun challenge, try to apply the law of conservation of mass to a scene from a Harry Potter film at this link: .

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physical changes in matter

A physical change in matter is a change in one or more of matters physical properties. Glass breaking is just one example of a physical change. Some other examples are shown in Figure 3.16 and in the video below. In each example, matter may look different after the change occurs, but its still the same substance with the same chemical properties. For example, smaller pieces of wood have the ability to burn just as larger logs do. MEDIA Click image to the left or use the URL below. URL: Because the type of matter remains the same with physical changes, the changes are often easy to undo. For example, braided hair can be unbraided again. Melted chocolate can be put in a fridge to re-harden. Dissolving salt in water is also a physical change. How do you think you could undo it?

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chemical changes in matter

Did you ever make a "volcano," like the one in Figure 3.17, using baking soda and vinegar? What happens when the two substances combine? They produce an eruption of foamy bubbles. This happens because of a chemical change. A chemical change occurs when matter changes chemically into an entirely different substance with different chemical properties. When vinegar and baking soda combine, they form carbon dioxide, a gas that causes the bubbles. Its the same gas that gives soft drinks their fizz. Not all chemical changes are as dramatic as this "volcano." Some are slower and less obvious. Figure 3.18 and the video below show other examples of chemical changes. MEDIA Click image to the left or use the URL below. URL:

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instructional diagrams

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questions

Which of the following is not a physical change in matter?

a. cutting paper

b. braiding hair

c. melting ice

-->  d. frying eggs

Which of the following is a physical change?

a. baking a cake

b. lighting a match

-->  c. tying a shoelace

d. burning a candle

Which of the following is not a chemical change in matter?

a. removing tarnish from copper

b. burning paper

-->  c. breaking glass

d. baking cupcakes

After a chemical change has occurred, matter

a. has less mass than before.

b. is the same substance as before.

-->  c. has different chemical properties than before.

d. all of the above

After a physical change, matter may

-->  a. look different.

b. have less mass.

c. have different chemical properties.

d. be an entirely different substance.

A sign that a chemical change has occurred is a change in

-->  a. color.

b. shape.

c. size.

d. all of the above.

An example of a chemical change is

a. cutting hair.

b. washing hair.

-->  c. bleaching hair.

d. none of the above.

What is true of matter after a chemical change?

a. It has more mass.

b. It is the same substance.

-->  c. It has different chemical properties.

d. Two of the above are true.

Which change in matter is easiest to reverse?

-->  a. chocolate melting

b. milk souring

c. leaves burning

d. iron rusting

Matter cannot be created or destroyed according to the law of

a. equal matter.

b. changes in matter.

-->  c. conservation of mass.

d. volume and mass.

Which of the following indicates a change in a chemical property of matter?

-->  a. Matter has a different color.

b. Matter consists of smaller pieces.

c. Matter has a different shape.

d. Matter has a different temperature.

When wood burns, it changes to

a. ashes.

b. carbon dioxide.

c. water vapor.

-->  d. all of the above.

type of change in which matter becomes an entirely different substance

a. physical change

-->  b. chemical change

c. law of conservation of mass

d. burning

e. sign of chemical change

f. mass

g. melting

example of a physical change

a. physical change

b. chemical change

c. law of conservation of mass

d. burning

e. sign of chemical change

f. mass

-->  g. melting

example of a chemical change

a. physical change

b. chemical change

c. law of conservation of mass

-->  d. burning

e. sign of chemical change

f. mass

g. melting

Making ice cubes with tap water is an example of a chemical change.

a. true

-->  b. false

amount of matter in a substance or object

a. physical change

b. chemical change

c. law of conservation of mass

d. burning

e. sign of chemical change

-->  f. mass

g. melting

All changes in matter can be reversed.

a. true

-->  b. false

type of change in which only physical properties of matter change

-->  a. physical change

b. chemical change

c. law of conservation of mass

d. burning

e. sign of chemical change

f. mass

g. melting

production of an odor

a. physical change

b. chemical change

c. law of conservation of mass

d. burning

-->  e. sign of chemical change

f. mass

g. melting

Melting metal changes it into an entirely different substance.

a. true

-->  b. false

matter cannot be created or destroyed

a. physical change

b. chemical change

-->  c. law of conservation of mass

d. burning

e. sign of chemical change

f. mass

g. melting

The release of gas bubbles is a sign of a chemical change.

-->  a. true

b. false

After a physical change, matter still has the same chemical properties.

-->  a. true

b. false

Cracking an egg shell is an example of a chemical change in matter.

a. true

-->  b. false

Crushing a metal can is an example of a physical change in matter.

-->  a. true

b. false

Physical changes in matter are often easy to reverse.

-->  a. true

b. false

Dissolving salt in water changes the water to an entirely different substance.

a. true

-->  b. false

All chemical changes are rapid and dramatic.

a. true

-->  b. false

Formation of a solid from a solution is a sign of a chemical change.

-->  a. true

b. false

To reverse a chemical change requires another chemical change.

-->  a. true

b. false

Boiling water is a chemical change because a gas is released.

a. true

-->  b. false

A sign of a chemical change is a change in mass.

a. true

-->  b. false

Matter can be created or destroyed if a chemical change occurs.

a. true

-->  b. false

diagram questions

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