Science Physical/Chemical Changes

Fireworks Exploding

Chemical Change- A chemical reaction occurs when fireworks combust, or explode. This reaction is what produces the flashes of light, the smoke, and the color changes. So, the change is chemical.

Mowing the Lawn

Physical Change- The blades of a lawnmower cut a blade of grass, the grass has simply been broken down into smaller parts, the chemicals that make up the grass don't go through a change.

Melting Butter for Popcorn

Physical Change- When butter or any other substance melts, it simply changes state from a solid to liquid. Changes of state of matter are always physical changes- the substance does not change its chemical composition when it changes state.

Reheating Leftover Food in a Microwave Oven

Physical Change- When food that has already been cooked is reheated, it simply increases in temperature- Chemical reactions occur when the food was first cooked, but when it is reheated no new chemical reactions take place. Therefore this change is physical.

A Log Decomposes

Chemical Change- When a log decomposes, it's molecules break down into new substances due to interactions with water, air, bacteria, fungi, etc. This makes decomposition a chemical change.

Silver or Brass Tarnishing

Chemical Change- When a metal tarnishes, it undergoes a chemical reaction due to long term exposure to the air. This exposure causes a reaction which changes the chemical composition of the surface of the metal. This makes the change a chemical change.

Solid is Added to a Beaker Containing Liquid

Chemical Change- When a new gas is produced, this gas is considered to be a new substance. The production of a new substance shows that a chemical reaction has occurred- the change is chemical.

Frying a Burger

Chemical Change- When food is cooked, its proteins undergo chemical reactions to form new substance. This makes any kind of cooking a chemical change.

Spoiling Food

Chemical Change- When food spoils, several different kinds of chemical reactions actually turn the food into new substances. This makes spoiling a chemical change.

Crushing Lifesaver into Powder

Physical Change- Doesn't change the types of atoms that make up the object, it's just broken down into smaller pieces.

Boiling an Egg in a Pot of Boiling Water

Chemical Change- Although the water does not undergo the chemical change when it is boiled, boiling food does not cause it to cook. When food is cooked, it's proteins undergo chemical reactions to form new substances. This means the change is a chemical change.

Burning Toast

Chemical Change- Any form of cooking causes a chemical reaction between the molecules of the food. Also burning involves combustion, which is another type of chemical reaction. Therefore, burning toast is a chemical change.

Stomach Digests Food

Chemical Change- In the process of digestion, chemicals such as enzymes and acids in your stomach break down your food into simpler chemicals. This makes the process of digestion a chemical reactions, so the change is chemical.

Protons Escape From the Nucleus of an Atom

Chemical Change- Radioactivity is when proton leave the nucleus of an atoms. When this occurs, the atom changes into a different element. Chemical changes are, by definition, changes in the types of elements that make up a substance. When an atoms changes into a different element, it is now a new chemical. The change is chemical.

Rusting Bicycle

Chemical Change- When iron rusts, it reacts with oxygen to create iron oxide. Iron oxide is a new substance that forms from the reaction between iron and oxygen-therefore the change is chemical, because a new substance has formed.

Old Milk Curdles

Chemical Change- When milk curdles, or spoils, it's proteins react and the milk becomes more acidic. This makes the chemical change.

Burning Leaves

Chemical Change- When something burns, it undergoes the process of combustion. This produces a new substance- if you have ever seen burnt leaves, or paper, or a log, you know that the burnt object has different properties from the original object. This shows that a chemical change has taken place.

Corroding Metal

Chemical Change- When the natal corrodes, substances that is comes in contact with (liquids, gases, etc.) reacts with the metal, turning it into a new substance with new properties. This makes corrosion a chemical change.

2 Substances are Mixed in a Beaker

Chemical Change- When two substances interact, and heat is produced, this heat is a sign that the substances have undergone an exothermic chemical reaction. The change is chemical.

Bleaching Your Hair

Chemical Change- Your hair bleaches when it undergoes a chemical reaction when exposed to certain substances (such as hydrogen peroxide and...?) Therefore, the change is chemical.

Glass Breaking

Physical Change- Breaking glass into smaller pieces is a physical change because the chemical composition (the types and combinations of atoms) of the glass doesn't change just because a larger piece of glass is broken into smaller pieces. Therefore the change is physical.

Freezing Chocolate Covered Bananas

Physical Change- Freezing any substance, be it water or a banana, only changes the state of matter in which the object is found. Although a banana is already a solid before it is frozen, it contains some water, and those water molecules can be frozen from a liquid into a solid. The rest of the molecules that make up a banana remain unchanged, so the banana has not undergone a chemical reaction. Therefore the change is physical.

Iced Tea Mix Added to Glass of Clear Water

Physical Change- In this case, the color change occurs only because the iced tea mix granules have dissolved, and spread out into the water. Dissolving does not make the iced tea granules change into a different chemical, in the granules do not chemically combined with the water. Therefore, just like any mixture, the change is physical.

Pouring Milk on Your Cereal

Physical Change- Pouring milk on oatmeal does not change the chemical composition of the oatmeal; no chemical reactions takes place when these two ingredients are mixed. They are for using milk to make the oatmeal less clumpy and more runny (or, in official scientific terms, making is less viscous) It is a physical change.

Cream Being Whipped

Physical Change- Whipping cream only changes its consistency (or its viscosity). The chemical composition of the cream is not changed- it just becomes less thick. Therefore the change is only physical.

Separating Sand From Gravel

Physical Change- Physically mixed, so physical change. Mixtures are always physical changes.

Boiling Water in a Pot on Kitchen Stove

Physical Change- The bubbles that form when water boils are at first bubbles released by the water, and later on in the process are water vapor bubbles. Gas is being released from a solution (water) and liquid turning into gas are both physical changes only- needs of the gases nor the water molecules turn into a new substance. The change is physical.

Melting Ice Cream

Physical Change- When ice cream changes state from a solid to a liquid, it has undergone the process if melting. Changes of state of matter, such as melting (or freezing, boiling) do not cause the matter to undergo a chemical change. Changes of state are always physical changes.

Squeezing Oranges to Make Orange Juice

Physical Change- When oranges are squeezed to produce our juice, this action simply releases, or un-mixes, the juice from the pulp of the orange. Since squeezing is a physical process, and squeezing produces the juice, this shows that the juice and the pulp of the orange are not chemically combined, and therefore no chemical reaction has taken place. The change is physical.

Mixing Salt into Water to Gargle

Physical Change- When salt is mixed with water, the salt particles dissolve into smaller particles that are too small to see. However, they do not chemically combine with the water. Therefore, the salt can quite easily be separated from the water (for example, by evaporation). Therefore the change is physical.