Changes in Matter

1
Changes in Matter

• Chapter 1, Lesson 3, Page E22

2
Essential Questions

• What is the difference between a physical and
  chemical change?
• How can physical and chemical changes be used to
  identify substances and to separate mixtures?
• What does the law of conservation of matter say?

3
Physical and Chemical Changes

• Changes in which no new substances are formed are
  physical changes. All changes in state are
  physical changes.
• When you shape clay on a potters wheel, you
  change its form. This is a physical change.
  Cutting up pieces of paper is also a physical
  change.
• But if an electric current is sent through water,
  a different kind of change takes place.

4
Physical and Chemical Changes

• Gases are produced, but the gases are not water.
  They are oxygen and hydrogen, the substances that
  make up water. In the space shuttles main
  engines, liquid oxygen and liquid hydrogen are
  mixed and burned as a fuel. Water a new
  substance is produced. Changes in which one or
  more new substances are formed are called
  chemical changes, or chemical reactions.

5
Marshmallows melting is a physical change.
Marshmallow burning, is a chemical change because
you have burnt it.
6
Physical and Chemical Changes

• Burning is a kind of chemical reaction. When
  charcoal burns, for example, carbon reacts with
  oxygen to produce carbon dioxide. Carbon and
  oxygen are the reactants, the starting substance
  in a chemical reaction. Carbon dioxide is a
  product of the reaction. It is the new substance.

7
Physical and Chemical Changes

• The ability of a substance to react chemically is
  called reactivity.
• There are some clues that can help you identify a
  chemical reaction. They include a change in color
  or the production of light, heat, or a gas.
• Paper turns black as it burns, for example. When
  baking soda is mixed with vinegar, it bubbles.
  This shows that carbon dioxide has been produced.
  A candle produces heat and light as it burns.

8
Physical and Chemical Changes

• Sometimes it is hard to tell the difference.
• Cherry-flavored drink powder is pale pink. When
  you mix it with water, it turns bright red. But
  the powder has only dissolved. It has gone
  through a physical change, not a chemical
  reaction. When you open a cold soft drink,
  bubbles are produced. But a chemical reaction has
  not taken place. The carbon dioxide has simply
  come out of the solution.
• Lets answer our questions.

9
When sodium combines with chlorine to make sodium
chloride (salt), light is produced. This new
product shows that a chemical reaction has
occurred.
Steel wool burns, but only in pure oxygen, not in
air. Steel wool is not as reactive as charcoal,
which does burn in air.
10
Using physical and chemical properties

• Chemical reactions often form products with
  properties that are different from those of the
  reactants.
• For example, when iron rusts, it turns red or
  brown.
• If you examine rust carefully, you will find that
  it is no longer shiny like iron. Rust is powdery,
  while iron bends and is easily formed into other
  shapes. Iron can conduct electricity, but rust
  cannot.

11
Using physical and chemical properties

• Therefore, a new substance has been formed. A
  chemical reaction has taken place.
• Chemical properties are also important in
  deciding how certain substances can be used.
• For example, many solutions are either acids or
  bases. Acids are sour, and weak acids can be used
  to flavor foods. Weak bases can be used in
  cleaning products. However, strong acids and
  strong bases are dangerous!
• Physical and chemical properties can also be used
  to separate mixtures or to identify substances in
  mixtures.

12
Iron is a shiny metal.
Rust is not shiny but instead red and powdery.
Now lets answer the questions.
13
Health LinkHeartburn

• Many people suffer from a condition called
  hartburn, which has nothing to do with the heart.
  The discomfort of heartburn is caused by a strong
  acid hydrochloric acid produced as a
  digestive juice by the stomach. Heartburn occurs
  when the acid backs up into the esophagus, or
  food tube, which leads from the mouth down to the
  stomach. To counter the discomfort, people
  swallow medications that contain a weak base,
  such as bicarbonate of soda. The base reacts with
  the acid to produce carbon dioxide and salt or
  other harmless substances.

14
(No Transcript)
15
Conservation of Matter

• Matter is neither created nor destroyed during a
  physical change or a chemical change. Scientists
  call this the law of conservation of matter.
• This law is easier to prove for some changes that
  it is for others. If you cut a piece of paper
  into tiny pieces, you have not made more paper.
  However, when water changes from a liquid to a
  gas, there may appear to be more matter because
  the volume of water vapor is greater. But no new
  matter has been produced.

16
Conservation of Matter

• It may be harder to believe that matter is not
  produced or destroyed during a chemical change.
  The reactants seem to disappear and the products
  seem to appear.
• However, in the 1700s, Antoine Lavoisier, a
  French chemist, was among the first scientists to
  carefully measure chemical reactions. He found
  that during a chemical change, the mass of the
  products equals the mass of the reactants.
  Because there is no change in mass after a
  chemical reaction, there Is not more and no less
  matter than there was before the reaction.
• Lets answer our questions.

17
Summary

• Physical changes do not result in the formation
  of new substances. However, new substances are
  formed during chemical changes. Physical and
  chemical properties can be used to identify
  substances and to separate mixtures. Matter is
  neither produced nor destroyed during physical
  and chemical reactions.
• Lets answer questions 1-2, 4-5 together orally
  from page E27 as well as our essential questions.