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Chemical Changes: Crash Course Kids #19.2

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It's the F ourth of July in Providence, Rhode Island. Brilliantfireworks are exploding in the night sky. When you look at the fireworks, you see dazzling sparkles of red, white and blue trickle down in all directions.

The explosion of fireworks is an example of chemical change.

During a chemical change, substances are changed into different substances. Another words, the composition of the substance changes.

Signs of Chemical Changes
How can you tell whether a change is a chemical change?
If you think you are unfamiliar with chemical changes, think again.

Physical changes are relatively easy to identify. If only the form of a substance changes, you have observed a physical change.

A common physical change occurs when matter changes from one phase to another. When an ice cube melts for example, it becomes liquid water. The solid ice and liquid water have the same composition. The only difference is the form.

C ol o r Changes

As in the case of autumn leaves, a change in color is a clue to indicate a chemical change.

Perhaps you have found a half eaten apple that turns brown. The reason is that a chemical change has occurs when food spoils.

You have just witnessed a spectacular chemical change if you have seen the leaves change color in the autumn.

When you bake a cake, energy is absorbed by the batter as it changes form a runny mix into a cake.
Energy - Absorbed or Released

Another sign of a chemical change is the release or gain of energy by an object. Many substances absorb energy to undergo a chemical change. Energy is absorbed during chemical changes involved in cooking, like baking a cake.

Energy can also be released during a chemical change. The fireworks that were mentioned above release energy in a form of light that you can see.

You can also see that energy is released when in this movie clip when sodium and chlorine are combined with water.

Odor Changes

It only takes one experience with a rotten egg to learn that they smell different that fresh eggs. When eggs and food spoil, they undergo a chemical change. The change in odor is a clue to the chemical change

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When you smell an odd order in foods such as chicken, pork of mayonnaise, you know that the food has undergone a chemical change. You can use this clue to avoid eating spoiled food and becoming ill.

Production of Gases or Solids

The formation of a gas is a clue to chemical changes. The bubbles of gas that you observed form when an antacid is dropped into water is an example of change.

Another clue that a chemical change has occurred is the formation of a solid. A solid that separates out of solution during a chemical change is called a precipitate.

As wood burns, it turns into a pile of ashes and gases that rise into air. After the wood is burned, it cannot be restored to its original form as a log.
Not easily reversed

How do physical and chemical changes differ from each other? Think about ice for a moment. After ice melts into liquid water, you can refreeze it into solid ice if the temperature drops. Freezing and melting are physical changes. The substances produced during chemical changes however cannot easily change back into the original substances.

Chemical vs Physical Change

The most important thing for your to remember is that in a physical change the composition of a substance does not change and in a chemical change the composition of a substance does change.

Chemical Reactions

Chemical Changes are also called Chemical Reactions. Chemical reactions involve combining different substances. The chemical reaction produces a new substance with new and different physical and chemical properties.

Matter is destroyed or created in chemical reactions. The particles of one substance are rearranged to form a new substance. never The same number of particles that exist before the reaction exist after the reaction.

To create your own chemical change, click on Fireworks. To find more fun information about firework displays that you see click here.

Consumer fireworks are illegal to possess in Rhode Island, however there are still plenty of opportunities to enjoy a great show. Although it rarely happens, it is possible that a firework component might fall to the ground without exploding. What do you do?

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It's the F ourth of July in Providence, Rhode Island. Brilliantfireworks are exploding in the night sky. When you look at the fireworks, you see dazzling sparkles of red, white and blue trickle down in all directions. The explosion of fireworks is an example of chemical change.

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Physical changes involve states of matter and energy. No new substance is created during a physical change, although the matter takes a different form. The size, shape, and color of matter may change. Physical changes occur when substances are mixed but don't chemically react.

How to Identify a Physical Change

One way to identify a physical change is that such a change may be reversible, especially a phase change. For example, if you freeze water into an ice cube, you can melt it into the water again. Ask yourself:

Is the change reversible? Not all physical changes are easy to reverse.

Was there a color change (with exceptions), bubble formation, or formation of a precipitate? These are all signs of a chemical change, not a physical change.

Is the chemical identity of the end product the same as it was before the change? If the answer is yes, it's a physical change. If the answer is no, it's a chemical change.

Examples of Physical Changes

Remember, the appearance of matter changes in a physical change, but its chemical identity remains the same.

Crushing a can

Melting an ice cube

Boiling water

Mixing sand and water

Breaking a glass

Dissolving sugar and water

Shredding paper

Chopping wood

Mixing red and green marbles

Sublimation of dry ice

Crumpling a paper bag

Melting solid sulfur into liquid sulfur. This is an interesting example since the state change does cause a color change, even though the chemical composition is the same before and after the change. Several nonmetals, such as oxygen and radon, change color as they change phase.

Chopping an apple

Mixing salt and sand

Filling a candy bowl with different candies

Vaporizing liquid nitrogen

Mixing flour, salt, and sugar

Mixing water and oil

Indications of a Chemical Change

Sometimes the easiest way to identify a physical change is to rule out the possibility of a chemical change. There may be several indications that a chemical reaction has occurred. Note: It's possible for a substance to change color or temperature during a physical change.

Evolving bubbles or releasing gas

Absorbing or releasing heat

Changing color

Releasing an odor

Inability to reverse the change

Precipitation of a solid from a liquid solution

Formation of a new chemical species. This is the best and surest indicator. A change in the chemical properties of the sample may indicate a chemical change (e.g., flammability, oxidation state).

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Examples of Physical Changes Compared With Chemical Changes

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Physical changes involve states of matter and energy. No new substance is created during a physical change, although the matter takes a different form. The size, shape, and color of matter may change. Physical changes occur when substances are mixed but don't chemically react.

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noun Chemistry.

a usually reversible change in the physical properties of a substance, as size or shape: Freezing a liquid is a physical change.

QUIZZES

CHALLENGE YOURSELF WITH THIS FUN HIGH SCHOOL STORIES VOCAB QUIZ!

If your language skills aren't already top-notch, then this vocab quiz can get you up to speed!

Words nearby physical change

physic, physical, physical allergy, physical anthropology, physical capital, physical change, physical chemistry, physical diagnosis, physical education, physical examination, physical geography

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

HOMEWORK HELP

What is a physical change?

A physical change is a change to the physical-as opposed to chemical-properties of a substance. They are usually reversible.

The physical properties of a substance include such characteristics as shape (volume and size), color, texture, flexibility, density, and mass.

Physical changes are not to be confused with chemical changes, which form whole new substances.

Physical change vs. chemical change

What do tearing paper, chopping wood, and boiling water all have in common? They're all physical changes. Physical change is an important concept in chemistry; it describes changes to things that don't result in brand-new substances.

Physical change upholds the molecular structure of a substance. Water, for example, is composed of two hydrogen molecules and one oxygen molecule, no matter whether it's boiling or frozen. You can change the physical state of water (for example, going from liquid to frozen) without impacting its underlying molecular structure.

A chemical change, in contrast, does impact a substance's molecular structure: one substance becomes another in a way that's usually irreversible. The reaction of iron and oxygen forms a whole new substance: rust.

Dissolving salt in water is an example of a physical change. The salt crystals have changed their physical (not chemical) state, and if you evaporate the water by boiling it, the salt will recrystallize and "magically" appear in the bottom of the pot.

Physical changes are all around us. They happen when ice forms or when metals form an alloy, like bronze and stainless steel. The distinction between physical and chemical changes is also a foundational concept in chemistry.

Can't remember the differences in physical versus chemical change? Here's a trick:

The initials of the phrase the very special cows meet daily stand for texture, volume, size, color, mass, and density. These are physical properties of a substance, and changes to them mark physical changes.

What are real-life examples of physical change?

What other words are related to physical change?

Which of the following is not a physical change?

A. Wood catching fire
B. Crumpling paper
C. Melting ice
D. Dissolving sugar in water

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Definition of physical change | Dictionary.com

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a usually reversible change in the physical properties of a substance, as size or shape: Freezing a liquid is a physical change. CHALLENGE YOURSELF WITH THIS FUN HIGH SCHOOL STORIES VOCAB QUIZ! If your language skills aren't already top-notch, then this vocab quiz can get you up to speed!

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Chemical change definition, a usually irreversible chemical reaction involving the rearrangement of the atoms of one or more substances and a change in their chemical properties or composition, resulting in the formation of at least one new substance: The formation of rust on iron is a chemical change. See more.

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Physical change

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Chemical change