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?

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

Vocabulary: • physical change • thermal energy • chemical change • endothermic change • law of conservation of mass • exothermic change • temperature • energy

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. ____________________ ____________________

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.

Figure 6 ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 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.