Physical and Chemical Change Card Sort #2 (Green)

Denting a piece of metal

Physical change The shape of the metal is changed but the identity of the substance does not change.

Sodium Metal is sliced in two

Physical change The shape of the metal is changed but the identity of the substance does not change.

Dying your hair

Both Temporary dye deposits acidic dyes on the outside of the hair shaft. As long as no peroxide is used, this process is physical. Permanant dye requires peroxide which breaks chemical bonds in the hair, releasing sulfur, which accounts for the characteristic odor of hair coloring products. Permanant hair colorants bond to the hair cuticle.

A substance gives off a green flame when burned

Chemical Change Flame tests are unique in that the change that occurs is temporary. When certain metal ions are heated, the electrons begin to jump around and release photons of light in different colors. When the source of heat is removed, the ions return to their original state, although some additional compounds may be formed through heating (reaction with oxygen).

Rust forming on a bike

Chemical Change Rust forms when iron reacts with oxygen in the air in the presence of water. An new substance called Iron Oxide is formed - this is rust.

Ice melts when salt is sprinkled on it.

Chemical and Physical Chemical - Road salt is a compound called calcium chloride. When this combound dissolves, it produces ions that interact with the water molecules and this interaction releases energy in the form of heat. Physical - Ice melts to form water. This is a phase change.

Alka-Seltzer Tablets in water

Chemical change Alka-Seltzer tablets contain aspirin, citric acid, and sodium bicarbonate (NaHCO3). When these tablets are dropped in water, the bicarbonate reacts with the hydrogen from the citric acid to form water and carbon dioxide gas. The fizzing you see is release of CO2 gas.

Burning leaves

Chemical change Burning leaves is an example of combustion. All combustion (explosions and fires) are chemical. Combustion requires oxygen and is the reaction of a substance (usually containing carbon) with oxygen in the air to produce carbon dioxide and water vapor. Soot and smoke are the the result of material that has not completely burned.

Two clear liquids are mixed and as a result turn pink.

Chemical change Color change is an indicator of chemical change. There was no dye added to the mixture and neither of the liquids was pink before. This means a new substance was created.

Frying an egg

Chemical change Cooking is always a chemical change. Heat causes proteins, carbohydrates and fats to crosslink, breakdown and change their structure in other ways.

Fireworks exploding

Chemical change Fireworks exploding is an example of combustion. All combustion (explosions and fires) are chemical. Combustion is the reaction of a substance (usually containing carbon) with oxygen and one of the product is always heat energy. The colors of fireworks are produced when the energy release is absorbed by different kinds of metal ions.

Rotting meat

Chemical change Rotting can involve breaking down of the chemical compounds that make up meat (proteins and fats). It can also involve the digestion of the meat by bacteria. In both cases new chemical compounds are produced. Rotting meat changes in color and smells bad. These are both signs of chemical change.

A substance begins to smoke when coming into contact with air

Chemical change Smoking would be a sign of combustion and heat production. Another sign that this is combustion is that the reaction requires air (oxygen). Combustion is always a chemical reaction.

A brick wall eroding from acid rain

Chemical change Sulfur dioxide (SO2) and nitrogen oxides (NOX) are forms of air pollution. These chemicals react with water, oxygen and other chemicals to form sulfuric and nitric acids. These acids can react with all different kinds of materials including the brick and break apart the chemical bonds of the molecules that make up these materials. This is called corosion.

Substance reacts with acid to form hydrogen gas.

Chemical change The hydrogen gas produced is a new substance. This means there is a chemical reaction.

When heated, a substance forms gas bubbles that smell like rotten eggs.

Chemical change There are two signs of a chemical reaction here. 1.) Gas production is indicated by bubbling of the liquid 2.) A change in odor indicates that the gas is a new substance.

Vinegar + baking soda = carbon dioxide bubbles

Chemical change There is a new substance formed (carbon dioxide), so this is a chemical reaction.

wood begins to rot

Chemical change When something rots, the substances that make up that material are changing into new substances. This is why the wood may show changes in color, hardness, and smell.

Glass breaking

Physical Changes of shape and form are always physical if the identity of the substance doesn't change. Glass is a brittle material so it breaks, but the pieces are still glass.

Water evaporating from a pool

Physical Change Evaporation means that water is going from liquid to gas phase (water vapor is a gas). This is a phase change.

A child blows on the window and frost forms.

Physical Change Frost is water vapor, or water in gas form, that becomes solid. The child's warm breath contains water vapor. When the water vapor hits the freezing cold glass of the window, it instantly freezes (forms solid frost). The process of going directly from gas to solid is called deposition.

A snowbank sublimes in January

Physical Change Sublimation is the direct change from solid phase to gas phase. All phase changes are physical. The identity of the substance does not change.

Changing from a solid to a liquid

Physical change Another word for this is melting and it is a phase change. Every substance has both a solid and liquid phase depending on temperature and pressure. Metals metal at very high temperatures.

A paper is torn in half.

Physical change Changes of shape and form are always physical if the identity of the substance doesn't change.

Crushing a soda can

Physical change Crushing is a change of form. Changes of shape and form are always physical if the identity of the substance doesn't change. (the metal that the can is made out of has not changed into a new substance)

Cutting your hair

Physical change Cutting is a change of form. Changes of shape and form are always physical if the identity of the substance doesn't change. (your hair is still hair)

Mixing salt and water

Physical change Dissolving is a physical change. You still have salt and water, and you can evaporate the water and recover the salt.

Melting butter

Physical change Melting is a phase change from solid to liquid. Phase change is always a physical change because no new substances are created (butter is still butter). Every substance has both a solid and liquid phase depending on temperature and pressure.

Separating sand from gravel

Physical change Separating these substance is and example of physical separation by filtration or sorting. No new substances are created so this is a physical change.

Dissolving sugar in water

Physical change Solid sugar is in a crystalline form. When sugar dissolve the individual sugar molecules mix with the water molecules, but no new substances are created. Dissolving is a physical change.

sublimation

Physical change Sublimation is when a solid changes directly to a gas without going through a liquid phase. Under certain conditions, snow an ice can sublimate at high altitudes.

Dropping Mentos into a bottle of Coke

Physical change Surprisingly, this one is a physical change. Dissolved CO2 gas is what makes soft drinks fizzy. When we open the bottle or can, we release the pressure that keeps the CO2 dissolved. Mentos candy has a rough surface that helps the bubbles form more quickly. As a result, the bubbles form in a big rush and cause a bubble explosion! There are no new substances created.

Shredding paper

Physical change The form of the paper is changed but there is no new substance created.

A substance smells like almonds

Physical change The phenomenon of smell is physical. In order for us to smell something, some particle of the substance must change into the gas phase. Once in the gas phase, the fragrance molecules can move through the air and end up in our noses where they bind to our smell receptors.

A stone sinks in water

Physical change This is a physical process. No new substances are formed.

Hammering a wooden peg into a board

Physical change This is a physical process. No new substances are formed.

Boiling water

Physical change Water boils when it has reached a temperature where it is rapidly changing into a gas. The bubbles in boiling water are bubbles of water vapor. There is no new substance formed so this is phase change.

A piece of paper is red

Physical property Color is a physical property.

A mineral has a high luster

Physical property Luster is the ability to reflect light and there are a variety of different kinds of luster including: metallic shiny, metallic dull, glassy, and pearly. This is a physical property of a material that we observe.