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Learning Objectives
- Label a change as chemical or physical.
- List evidence that can indicate a chemical change occurred.
Change is happening all around us all of the time. Just as chemists have classified elements and compounds, they have also classified types of changes. Changes are classified as either physical or chemical changes. Chemists learn a lot about the nature of matter by studying the changes that matter can undergo. Chemists make a distinction between two different types of changes that they study—physical changes and chemical changes.
Physical Change
Physical changes are changes in which no bonds are broken or formed. This means that the same types of compounds or elements that were there at the beginning of the change are there at the end of the change. Because the ending materials are the same as the beginning materials, the properties (such as color, boiling point, etc.) will also be the same. Physical changes involve moving molecules around, but not changing them. Some types of physical changes include:
- Changes of state (changes from a solid to a liquid or a gas and vice versa).
- Separation of a mixture.
- Physical deformation (cutting, denting, stretching).
- Making solutions (special kinds of mixtures).
As an ice cube melts, its shape changes as it acquires the ability to flow. However, its composition does not change. Melting is an example of a physical change. A physical change is a change to a sample of matter in which some properties of the material change, but the identity of the matter does not. When liquid water is heated, it changes to water vapor. However, even though the physical properties have changed, the molecules are exactly the same as before. We still have each water molecule containing two hydrogen atoms and one oxygen atom covalently bonded. When you have a jar containing a mixture of pennies and nickels and you sort the mixture so that you have one pile of pennies and another pile of nickels, you have not altered the identity of the pennies or the nickels—you've merely separated them into two groups. This would be an example of a physical change. Similarly, if you have a piece of paper, you don't change it into something other than a piece of paper by ripping it up. What was paper before you started tearing is still paper when you are done. Again, this is an example of a physical change.
Physical changes can further be classified as reversible or irreversible. The melted ice cube may be refrozen, so melting is a reversible physical change. Physical changes that involve a change of state are all reversible. Other changes of state include vaporization (liquid to gas), freezing (liquid to solid), and condensation (gas to liquid). Dissolving is also a reversible physical change. When salt is dissolved into water, the salt is said to have entered the aqueous state. The salt may be regained by boiling off the water, leaving the salt behind.
Chemical Change
Chemical changes occur when bonds are broken and/or formed between molecules or atoms. This means that one substance with a certain set of properties (such as melting point, color, taste, etc) is turned into a different substance with different properties. Chemical changes are frequently harder to reverse than physical changes.
One good example of a chemical change is burning a candle. The act of burning paper actually results in the formation of new chemicals (carbon dioxide and water) from the burning of the wax. Another example of a chemical change is what occurs when natural gas is burned in your furnace. This time, on the left there is a molecule of methane, \(\ce{CH_4}\), and two molecules of oxygen, \(\ce{O_2}\); on the right are two molecules of water, \(\ce{H_2O}\), and one molecule of carbon dioxide, \(\ce{CO_2}\). In this case, not only has the appearance changed, but the structure of the molecules has also changed. The new substances do not have the same chemical properties as the original ones. Therefore, this is a chemical change.
We can't actually see molecules breaking and forming bonds, although that's what defines chemical changes. We have to make other observations to indicate that a chemical change has happened. Some of the evidence for chemical change will involve the energy changes that occur in chemical changes, but some evidence involves the fact that new substances with different properties are formed in a chemical change.
Observations that help to indicate chemical change include:
- Temperature changes (either the temperature increases or decreases).
- Light given off.
- Unexpected color changes (a substance with a different color is made, rather than just mixing the original colors together).
- Bubbles are formed (but the substance is not boiling—you made a substance that is a gas at the temperature of the beginning materials, instead of a liquid).
- Different smell or taste (do not taste your chemistry experiments, though!).
- A solid forms if two clear liquids are mixed (look for floaties—technically called a precipitate).
Example \(\PageIndex{1}\)
Label each of the following changes as a physical or chemical change. Give evidence to support your answer.
- Boiling water.
- A nail rusting.
- A green solution and colorless solution are mixed. The resulting mixture is a solution with a pale green color.
- Two colorless solutions are mixed. The resulting mixture has a yellow precipitate.
Solution
- Physical: boiling and melting are physical changes. When water boils, no bonds are broken or formed. The change could be written: \(\ce{H_2O} \left( l \right) \rightarrow \ce{H_2O} \left( g \right)\)
- Chemical: The dark grey nail changes color to form an orange flaky substance (the rust); this must be a chemical change. Color changes indicate chemical change. The following reaction occurs: \(\ce{Fe} + \ce{O_2} \rightarrow \ce{Fe_2O_3}\)
- Physical: because none of the properties changed, this is a physical change. The green mixture is still green and the colorless solution is still colorless. They have just been spread together. No color change occurred or other evidence of chemical change.
- Chemical: the formation of a precipitate and the color change from colorless to yellow indicate a chemical change.
Exercise \(\PageIndex{1}\)
Label each of the following changes as a physical or chemical change.
- A mirror is broken.
- An iron nail corroded in moist air
- Copper metal is melted.
- A catalytic converter changes nitrogen dioxide to nitrogen gas and oxygen gas.
- Answer a:
- physical change
- Answer b:
- chemical change
- Answer c:
- physical change
- Answer d:
- chemical change
Separating Mixtures Through Physical Changes
Homogeneous mixtures (solutions) can be separated into their component substances by physical processes that rely on differences in some physical property, such as differences in their boiling points. Two of these separation methods are distillation and crystallization. Distillation makes use of differences in volatility, a measure of how easily a substance is converted to a gas at a given temperature. A simple distillation apparatus for separating a mixture of substances, at least one of which is a liquid. The most volatile component boils first and is condensed back to a liquid in the water-cooled condenser, from which it flows into the receiving flask. If a solution of salt and water is distilled, for example, the more volatile component, pure water, collects in the receiving flask, while the salt remains in the distillation flask.
Mixtures of two or more liquids with different boiling points can be separated with a more complex distillation apparatus. One example is the refining of crude petroleum into a range of useful products: aviation fuel, gasoline, kerosene, diesel fuel, and lubricating oil (in the approximate order of decreasing volatility). Another example is the distillation of alcoholic spirits such as brandy or whiskey. This relatively simple procedure caused more than a few headaches for federal authorities in the 1920s during the era of Prohibition, when illegal stills proliferated in remote regions of the United States.
Another example for using physical properties to separate mixtures is filtration (Figure \(\PageIndex{4}\)). Filtration is any mechanical, physical or biological operation that separates solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass. The fluid that passes through is called the filtrate. There are many different methods of filtration; all aim to attain the separation of substances. Separation is achieved by some form of interaction between the substance or objects to be removed and the filter. The substance that is to pass through the filter must be a fluid, i.e. a liquid or gas. Methods of filtration vary depending on the location of the targeted material, i.e. whether it is dissolved in the fluid phase or suspended as a solid.
Summary
- Chemists make a distinction between two different types of changes that they study—physical changes and chemical changes.
- Physical changes are changes that do not alter the identity of a substance.
- Chemical changes are changes that occur when one substance is turned into another substance.
- Chemical changes are frequently harder to reverse than physical changes. Observations that indicate a chemical change has occurred include color change, temperature change, light given off, formation of bubbles, formation of a precipitate, etc.
Contributions & Attributions
Boundless (www.boundless.com)
FAQs
What are physical and chemical changes in matter? ›
Physical changes are those in which the shape, size, or state of the matter changes, but the substance is still essentially the same. For example, chopping up a carrot or ice melting into water are both physical changes. Chemical changes are those where one or more substances are combined to produce a new substance.
What are 3 physical changes and 3 chemical changes? ›Examples of chemical changes would be burning, cooking, rusting, and rotting. Examples of physical changes could be boiling, melting, freezing, and shredding. Most physical changes can be reversed if sufficient energy is provided.
What are 3 physical changes of matter? ›Types of some physical changes are texture, shape, temperature, and a change in the state of matter.
What are the 5 changes in physical matter? ›Changes in the size or form of matter are examples of physical change. Physical changes include transitions from one state to another, such as from solid to liquid or liquid to gas. Cutting, bending, dissolving, freezing, boiling, and melting are some of the processes that create physical changes.
What are physical and chemical changes answers? ›In a physical change the appearance or form of the matter changes but the kind of matter in the substance does not. However in a chemical change, the kind of matter changes and at least one new substance with new properties is formed.
What are 5 chemical changes matter? ›The five conditions of chemical change: color change, formation of a precipitate, formation of a gas, odor change, temperature change.
What are 3 examples of a physical change? ›Some common examples of physical changes are: melting, freezing, condensing, breaking, crushing, cutting, and bending. Some, but not all physical changes can be reversed.
What are 3 chemical changes? ›Burning, cooking, rusting and rotting are examples of chemical changes.
What are 5 examples of both physical and chemical changes? ›Examples of chemical changes are burning, cooking, rusting, and rotting. Examples of physical changes are boiling, melting, freezing, and shredding. Many physical changes are reversible, if sufficient energy is supplied.
What are 2 examples of chemical change? ›Examples of chemical changes include baking soda and vinegar creating carbon dioxide, iron rusting, and wood burning. The body creates a variety of chemical reactions as well, including the metabolization of food and the combination of sugar and saliva creating amylase.
What are 3 different examples of physical properties of matter? ›
Familiar examples of physical properties include density, color, hardness, melting and boiling points, and electrical conductivity.
What are the 6 chemical changes? ›...
- Combination Reaction. ...
- Decomposition Reaction. ...
- Displacement Reaction. ...
- Double Displacement Reaction. ...
- Precipitation Reaction.
A physical change involves a change in physical properties. Examples of physical properties include melting, transition to a gas, change of strength, change of durability, changes to crystal form, textural change, shape, size, color, volume and density.
What are physical changes answers? ›A physical change is a type of change in which the form of matter is altered but one substance is not transformed into another. An example of a physical change is crumpling a sheet or paper or breaking a pane of glass or freezing water into ice.
What are the 10 physical chemical properties? ›Physical properties of matter include color, hardness, malleability, solubility, electrical conductivity, density, melting point, and boiling point.
What is the physical change and give one example answer? ›No new products are formed during the physical change of a matter. These changes are only temporary and mostly reversible in nature. Examples are boiling water, crushing a can, melting ice, dissolving salt/sugar in water etc.
What are the 4 Changes in matter? ›Physical changes that involve a change of state are all reversible. Other changes of state include vaporization (liquid to gas), freezing (liquid to solid), and condensation (gas to liquid). Dissolving is also a reversible physical change.
What are types of chemical changes? ›The five basic types of chemical reactions are combination, decomposition, single-replacement, double-replacement, and combustion.
What are 5 examples of chemical properties matter? ›Flammability, toxicity, acidity, the reactivity of various types, and heat of combustion are examples of chemical properties.
What is a common physical change? ›Common physical changes include melting, change of size, volume, color, density, and crystal form.
What causes matter change? ›
Adding or removing energy from matter causes a physical change as matter moves from one state to another. For example, adding thermal energy (heat) to liquid water causes it to become steam or vapor (a gas). And removing energy from liquid water causes it to become ice (a solid).
What are the 3 basic chemical reactions? ›There are three main types of chemical reactions important in human physiology, synthesis (anabolic), decomposition (catabolic) and exchange.
What is the most common chemical change? ›Common Chemical Changes
Change color. Change temperature. Produce bubbles. Produce precipitate (in liquids)
The process of burning (as opposed to evaporating) is a chemical reaction, a chemical change.
What are examples of physical and chemical changes at the same time? ›burning a candle is an example where both physical and chemical changes occur simultaneously.
What is an example of physical change and chemical change together? ›The burning of wood is an example of a change that is both chemical and physical. When heated, the moisture in the wood turns to vapour, which is a physical change. Burning wood produces carbon dioxide (among other products) and results in a chemical change.
Which of the following are both physical and chemical change? ›Assertion :The burning of a candle is both a physical and a chemical change.
Is color change a chemical change? ›Color. The changing of color of a substance is not necessarily an indicator of a chemical change. For example, changing the color of a metal does not change its physical properties. However, in a chemical reaction, a color change is usually an indicator that a reaction is occurring.
What are 20 examples of chemical changes? ›- burning of paper.
- cooking of food.
- burning of wood.
- ripening of fruits.
- rotting of fruits.
- frying egg.
- rusting of iron.
- mixing acid and base.
- Destroying a can.
- Melting of ice cubes.
- Heating water.
- Combining water and sand.
- Shattering glass.
- Dissolving water and sugar.
- Tearing up paper.
- Making woodcuts.
Is an example of physical change *? ›
A physical change is one where there are changes only in the physical properties of the components. For example, when a pure gold ingot is melted, then it changes from solid gold to liquid gold.
What are 3 physical and chemical properties? ›Physical properties include color, density, hardness, and melting and boiling points. A chemical property describes the ability of a substance to undergo a specific chemical change.
What are 4 common physical properties? ›Familiar examples of physical properties include density, color, hardness, melting and boiling points, and electrical conductivity.
What are 7 examples of physical properties? ›Examples of physical properties are: color, smell, freezing point, boiling point, melting point, infra-red spectrum, attraction (paramagnetic) or repulsion (diamagnetic) to magnets, opacity, viscosity and density. There are many more examples.
What are the top 5 chemical reactions? ›The five major types of chemical reactions are synthesis, decomposition, single replacement, double replacement, and combustion. A composition reaction produces a single substance from multiple reactants.
What is a chemical change 7th grade? ›Chemical changes are permanent changes which happen to the original substances making it lose its inherent properties. Changes like these are irreversible like – rusting of iron, burning of wood.
What are the 7 signs of a chemical change? ›- Change in Color.
- Formation of a Gas.
- Formation of a Precipitate.
- Change in Odor.
- Change in Temperature.
- Something is Burning.
- Light is Being Produced.
- Deconstructing a box after a delivery.
- Cutting an old credit card into pieces.
- Cutting your hair.
- Sharpening a pencil.
- Crocheting yarn into a blanket.
- Melting crayons.
- Shredding paper.
- Cutting an old t-shirt.
Some physical changes that matter can go through are breaking, melting, freezing, cutting, crushing and dissolving.
What is a physical change 8th grade? ›In a physical change, matter does NOT change into a new kind of matter. An example of a physical change is a change of state, like melting ice from solid to liquid. If you boil water on the stove, that is a physical change. Boiling water is a change of state from liquid to gas.
What are 22 states of matter? ›
- 4.1 Superconductor.
- 4.2 Superfluid.
- 4.3 Bose–Einstein condensate.
- 4.4 Fermionic condensate.
- 4.5 Rydberg molecule.
- 4.6 Quantum Hall state.
- 4.7 Photonic matter.
- 4.8 Dropleton.
Considering all the studies that have been done till today, there are 22 states of matter in total described below: Solid: a solid holds a definite shape and volume without a container and its particles are held very close to each other.
What are the 5 types of matter? ›Hint: There are five states of matter which are solid, liquid, gas, plasma, Bose-Einstein condensate.
What are 2 examples of chemical changes in matter? ›Burning, cooking, rusting and rotting are examples of chemical changes.
What is an example of chemical change in matter? ›- Burning wood.
- Souring milk.
- Mixing acid and base.
- Digesting food.
- Cooking an egg.
- Heating sugar to form caramel.
- Baking a cake.
- Rusting of iron.
Examples of physical change include changes in the size or shape of matter. Changes of state, for example, from solid to liquid or from liquid to gas, are also physical changes. Some of the processes that cause physical changes include cutting, bending, dissolving, freezing, boiling, and melting.
What are 3 examples of a chemical change? ›Examples of chemical changes include baking soda and vinegar creating carbon dioxide, iron rusting, and wood burning. The body creates a variety of chemical reactions as well, including the metabolization of food and the combination of sugar and saliva creating amylase.
What are the main chemical changes? ›The five basic types of chemical reactions are combination, decomposition, single-replacement, double-replacement, and combustion.
What are three types of chemical change? ›There are three main types of chemical reactions important in human physiology, synthesis (anabolic), decomposition (catabolic) and exchange.
What can cause a chemical change? ›Chemical changes occur when bonds are broken and/or formed between molecules or atoms. This means that one substance with a certain set of properties (such as melting point, color, taste, etc) is turned into a different substance with different properties.
Is growth a chemical or physical change? ›
Growth results in increase in size due to the intake of food. The food consumed by a living organism, is absorbed by the body and is used to nourish the cells for growth. Therefore, this is a chemical change, which includes the formation of new substances during the process of growth.
What are the 6 types of chemical changes? ›...
- Combination Reaction. ...
- Decomposition Reaction. ...
- Displacement Reaction. ...
- Double Displacement Reaction. ...
- Precipitation Reaction.
| Physical Change | Chemical Change |
|---|---|
| 1. Making salt from seawater | 1. Moldy bread |
| 2. Shattered glass | 2. Burning wood |
| 3. Tearing a newspaper | 3. Cooking food |
| 4. Cutting meat, fruits, and vegetables | 4. Fossilization |