1.4 - Changes in Matter
What Happens to a Substance in a Physical Change?
What Happens to a Substance in a Chemical Change?
How are Changes in Energy and Matter Related?
Vocabulary:
• physical change
• chemical change
• law of conservation of mass
• temperature
• thermal energy
• endothermic change
• exothermic change
• energy
What Happens to a Substance in a Physical Change?
How can matter change? In a physical change, the form or appearance of the matter is altered, but the
substance in the matter does not turn into a different substance. In Figure 1, a butter artist has changed a
block of butter into a sculpture. Even though it looks different, the figure is still butter.
A substance
that undergoes a physical change is still the same substance after the change. Another example of a physical
change is snow or ice cream melting.
Figure 1 ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙
Changes of State
Matter occurs in three states – solid, liquid, and gas. Suppose it rains and a puddle is
formed on your driveway. When you walk outside later that day, the puddle is gone! Has the liquid
disappeared? No, a physical change has occurred. The liquid water changed into water vapor (gas) and mixed
in with the air. When matter changes states (solid to a liquid, liquid to a gas, etc.), a physical change has taken
place.
Changes in Shape or Form
Is there a physical change when you dissolve a teaspoon of table salt in a
cup of water? To answer this question, you would need to figure out whether or not the salt has been turned
into a different substance. For example, the saltwater solution tastes salty, like the undissolved salt. If you
leave the saltwater solution in a tray and let the water evaporate, the salt will remain as crystals at the bottom
of the tray. The salt crystals do not look exactly like the salt that was put into the water, but it’s still salt.
Therefore, dissolving is a physical change. Bending, crushing, breaking, and chopping are other examples of
physical changes. Any change that alters the shape or form of matter is a physical change.
Figure 2 ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙
Appearance Changes - Origami paper folding involves physical changes.
1) Models - Using the corner of this page, make two physical changes to
the paper.
2) Communicate – Ask a partner to list the changes you made.
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3) Challenge – To make Kool-Aid, colored powder is dissolved into a pitcher of water. Is it correct to say that a
new substance, Kool-Aid, has been formed so it must not be a physical change?
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Assess Your Understanding
What Happens to a Substance in a Chemical Change?
Another kind of change happens when a substance turns into a different kind of substance. A
chemical change (or chemical reaction) occurs when a change in matter produces one or more
new substances. In some chemical changes, a single substance breaks down into two or more
different substances. For example, hydrogen peroxide breaks down into water and oxygen gas
when it’s rubbed on a cut on your skin.
Other times, two or more substances combine to form a different substance. In nature,
photosynthesis is a chemical change. Many compounds combine with the sun’s energy to
produce new substances.
Figure 3 shows chemical changes that are used in forensics to collect evidence at a crime scene. When a
detective “dusts for fingerprints”, he/she uses a process that requires a chemical reaction. To make the
fingerprints more visible, a chemical found in super-strong glue is heated. Vapors from
the glue react with body chemicals or sweat in the fingerprint to form a white powder
which makes the print visible. Luminol is a chemical that can react with traces of blood
that are too small to
see with the naked eye to form a new substance that glows in the dark.
Unlike a physical change, a chemical change produces
new substances with new and different properties.
Figure 3 ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙
Chemical Changes
The print is visible because of a
chemical change.
Examples of Chemical Change
The burning of natural gas on a gas stove is a common chemical
change. Natural gas is mostly made up of the compound methane (CH4). When natural gas burns, the
methane combines with oxygen in the air and forms new substances, like carbon dioxide (CO2) and water
vapor (H2O). Both of these new substances have different properties from those of methane. Combustion is
the chemical change that occurs when fuels, candle wax, or wood burn in air. Other processes resulting in
chemical change include electrolysis, oxidation, and tarnishing. Figure 4 describes each of these.
Figure 4∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙
Types of Chemical Change
The copper in the penny above is
exposed to oxygen in the air.
What chemical change did the
penny likely undergo? Describe the
properties before and after the
chemical change.
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Conservation of Mass
Water may seem to “disappear” when it evaporates, but scientists have proven
otherwise. In the 1770s, a French Chemist, Antoine Lavoisier, measured mass before and after a chemical
change. He found that the mass was the same before and after the change. This means that no mass was lost
or gained during the change. The law of conservation of mass (also known as the law of conservation of
matter) states that matter cannot be created or destroyed in a chemical or physical change.
Suppose you could measure all of the water and carbon dioxide produced when methane burns. You
would find that it equals the mass of the original methane plus the mass of the oxygen from the air that was
used in the burning. Figure 5 shows that during a chemical change, atoms are not lost or gained, only
rearranged.
Figure 5 ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙
Conservation of Mass
Count the atoms of
each element before
and after the chemical
chemical change. Is
mass conserved in this
reaction? Explain.
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Assess Your Understanding
How Are Changes in Energy and Matter Related?
Are there some days in which you feel that you are full of energy? Energy is the ability to do work or cause
change.
Every chemical and physical change in mater includes a change in energy. A change as simple
as bending a paperclip requires energy. When an ice cube changes to liquid water, it absorbs the energy from
its surroundings. When the wax of a candle burns, it gives off energy. The energy from a candle burning can
be seen as light and can be felt as heat.
Just like matter, energy is also conserved in a chemical change. Energy cannot be created or
destroyed. It can only be transformed from one form to another.
Temperature and Thermal Energy
Think of what it feels like to walk inside the air-conditioned
school from the outdoors on a hot day. Temperature is a measure of how hot or cold something is. The
temperature of a substance is related to the energy of motion of the particles of matter. The particles of gas
in the warm outside air have a greater average energy of motion than the particles of the cool air inside the
school.
Thermal energy is the total energy of the motion of all of the particles in an object. When you describe
a bowl of soup as hot or ice cream as cold, you are experiencing the thermal energy of the substance.
Temperature and thermal energy are not the same thing, but the amount of thermal energy an object has is
related to its temperature. Thermal energy naturally flows from warmer matter to cooler matter.
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Thermal Energy
Shade in the arrow that indicates which
direction energy will flow between the girl
and the icy water and the snowman and
the hot air.
Energy
Energy
Thermal Energy and Changes in Matter
Thermal energy is a form of energy that is often released
or absorbed when matter changes. For example, an ice cube absorbs the thermal energy from its
surroundings when it melts, leaving the surroundings feeling cold. That’s why you can pack food and drinks in
an ice-filled lunch bag. The melting of ice is called an endothermic change. An endothermic change is a
change in which energy is absorbed. An exothermic change is a change in which energy is given off or
released. Combustion is a chemical change that releases light and thermal energy.
Do the math!
A student records the temperature of two reactions once per minute. Her data are plotted on the graph.
1) What was the change in temperature for each
reaction after 10 minutes?
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2) On the graph, label each reaction as exothermic
or endothermic. Explain how you know.
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Indiana Jane and the Investigation of Matter
Indiana Jane is hunting for lost treasures of matter. Answer the questions about Indiana’s finding along the
way. Then, complete the notebook with the information you gathered.