Physical & Chemical Changes Changing Matter Physical & Chemical Changes
Lesson Goals and Objectives I can Explain what physical changes are and how matter can change from one state to another. Explain how chemical changes can cause some kinds of matter to become new matter. distinguish between a physical and chemical change.
Matter is anything with volume and mass. Reviewing Matter Matter is everywhere. Matter is anything with volume and mass. How we identify matter: Properties Matter has properties Two basic types of properties that we can associate with matter. Physical properties Chemical properties
electrical conductivity ductility color malleability Physical Properties Anything that can be observed without changing the identity of the substance. (Tends to be measurable.) melting point density boiling point thermal conductivity electrical conductivity ductility color malleability
Reactivity to other chemicals Chemical Properties The way a substance may change or react to form new substances heat of combustion Oxidation reactivity with water Flammability pH Reactivity to other chemicals Chemical properties of matter describes its "potential" to undergo some chemical change or reaction by virtue of its composition. What elements, electrons, and bonding are present to give the potential for chemical change. It is quite difficult to define a chemical property without using the word "change". Eventually you should be able to look at the formula of a compound and state some chemical property. At this time this is very difficult to do and you are not expected to be able to do it. For example hydrogen has the potential to ignite and explode given the right conditions. This is a chemical property. Metals in general have they chemical property of reacting with an acid. Zinc reacts with hydrochloric acid to produce hydrogen gas. This is a chemical property.
Matter is constantly experiencing both chemical and physical changes. Changing matter Matter is constantly experiencing both chemical and physical changes. Matter can be changed two ways Physically Chemically
Physical Changes A Physical change is a change in a substance that does not change the identity of the substance. no new substances are formed. Change in the form of a substance, not in its chemical composition. Substance may seem different, but the way the atoms link up is the same. A physical change alters the form of a substance, but does not change it to another substance. Physical changes are those changes that do not result in the production of a new substance. If you melt a block of ice, you still have H2O at the end of the change.
Physical Change – examples Change in size or shape Mass Volume Density weight Making a mixture 2 or more types of matter (substances) mixed together Not in specific amounts Can be separated physically Dilutions Dissolving
Physical Change – examples Change in phase Melting (solid to liquid) Boiling (liquid to gas) vaporation (liquid to gas) Condensation (gas to liquid) Freezing (liquid to solid) Sublimation (solid to gas) Deposition (gas to solid) In all three phases, water molecules are still intact. Motions of molecules and the distances between them change.
Physical Change Physical changes might be caused by: Grinding Cutting Crushing Bending Breaking Heating/cooling (change in phase) squishing
Physical Change Evidence that a physical change has occurred might include: Change in shape Change in form Change in size Change in phase (This is always a physical change!) Physical changes are usually reversible
If you remember, ice is water in the solid state. When you drop the ice cube into the liquid, it begins to melt because the temperature is higher than that of the ice cube. It's like putting a snowman on your front lawn in July. The ice cube becomes liquid water. This is an example of a physical change. The solid water turned to liquid water.
Physical Change
Special types of physical changes where any object changes state, such as when water freezes or evaporates, are sometimes called change of state operations.
More Examples of Physical Changes Change in size, shape, or color Pencil shavings Torn Paper Crushed ice Sugar dissolved in water Painting a wall
Can you think of ways that you can physically change a sheet of paper? Cutting Tearing Shredding Folding Painting Writing on Gluing
Physical change What could you do to these items to cause a physical change to occur?
Physical and Chemical Changes How to tell the difference
If you break a bottle, you still have glass If you break a bottle, you still have glass. Painting your nails will not stop them from being fingernails. Some common examples of physical changes are: melting, freezing, condensing, breaking, crushing, cutting, and bending.
Some, but not all physical changes can be reversed Some, but not all physical changes can be reversed. You could refreeze the water into ice, but you cannot put your hair back together if you don’t like your haircut!
Which of the following are physical properties? Concept check Which of the following are physical properties? liquid at room temperature reacts with metals to form H2 gas acids and bases combine to form water and a ‘salt’ boils at 145 degrees Celsius
CHEMICAL PROPERTIES Remember? Chemical properties can ONLY be observed AS the substances are changing into different substances.
Chemical Changes Chemical changes do alter the identity of a substance In other words, a chemical change is when something changes into an entirely different substance The composition of the substance changes. The substances present at the beginning of the change are not present at the end new substances are formed. The change cannot be “undone.”
Chemical change Chemical changes occur when a chemical reaction causes bonds between atoms to break or to form.
Atoms are re-arranged, NOT created or destroyed Chemical Changes Atoms are re-arranged, NOT created or destroyed
Examples of chemical changes When you burn a log in a fireplace, you are carrying out a chemical reaction that releases carbon. When you light your Bunsen burner in lab, you are carrying out a chemical reaction that produces water and carbon dioxide.
Reactivity How readily (easily) a substance combines chemically with other substances. Reactions between Substances Reactions with Acid Reactions with Oxygen Reactions with Electricity Vinegar + baking soda = release of Carbon Dioxide Gas OXIDATION Iron + Oxygen = rust Silver Plating Sodium + chloride = salt Silver + sulfur in the air = tarnish
WHAT’S THE POINT OF THIS? Reacts with acids There were a few horror movies made in the 70s, 80s, and 90s and even this decade starring these guys: Besides many gross events, one of the things the people in the movie quickly realize is that if you cut or damage one of these aliens, it bled a concentrated acid that would “melt” or “corrode” anything it came into contact with. Nasty. WHAT’S THE POINT OF THIS?
DEBUNKING THE MYTH Well, I think those movies have perpetuated a myth common to many people that acids are all super-harmful, extremely dangerous, eat-through-anything chemicals. Really? Here’s some examples of acidic compounds: So…not ALL acids are instant-death, huh. Now, some of those acids can be pretty powerful substances. The next time you lose a tooth or eat a chicken wing, soak that bone in coke for a few days and observe it…no wonder dentists don’t like soda. Acids (and their opposites…bases) are just reactive chemicals that behave in certain ways. Here are some common bases:
Is There a Point To This? Well, yeah. Acids and bases are just a few of MANY kinds of chemicals that can react with each other. When chemicals react, they rearrange their atoms & molecules to produce new substances. New substances! Chemical change! You’re familiar with baking soda and vinegar, right? And we all know that gas under high pressure can be fun…or deadly. They combine… They react and make a new substance (CO2 gas)
FLAMMABILITY: A material’s ability to BURN in the presence of OXYGEN
Other Examples Wood burning Metal rusting Food digesting Gasoline burning Cake baking Respiration Photosynthesis Decomposition Polymerization
Electrolysis of Water Copyright © Cengage Learning. All rights reserved
Electrolysis of Water Water decomposes to hydrogen and oxygen gases. Copyright © Cengage Learning. All rights reserved
Common Errors Ice melting, water freezing, water evaporating, and steam condensing are all examples of a state change. These are physical changes, not chemical. Diluting a solution is a physical change, even if the color becomes more faint.
Concept Check Pulverizing (crushing) rock salt Burning of wood How many of the following are examples of a chemical change? Pulverizing (crushing) rock salt Burning of wood Dissolving of sugar in water Melting a popsicle on a warm summer day 1 (burning of wood)
Concept Check Sugar fermenting to form ethyl alcohol Classify each of the following as a physical or chemical change. Sugar fermenting to form ethyl alcohol Iron metal melting Iron combining with oxygen to form rust chemical physical Sugar fermenting to form ethyl alcohol. Chemical change: describes how sugar forms a new substance (ethyl alcohol) via a chemical reaction. Iron metal melting. Physical change: describes a state change, but the material is still iron. Iron combining with oxygen to form rust. Chemical change: describes how iron and oxygen react to make a new substance, rust. Copyright © Cengage Learning. All rights reserved
How do we know if a chemical change has occurred? Possible Indicators of a Chemical Change Energy Release (a change in temperature heats up or cools down/light) ex: match burns, cold packs cool Forms bubbles or gas ex: vinegar + baking soda CO2 Permanent unexpected color change ex: burning wood changes its color odor released new gases ex: baking bread creates Irreversibility difficult to reverse ex: can’t turn a cookie back into dough Production of a gas ex: vinegar and baking soda produces CO2 Formation of a precipitate ex: vinegar and milk forms curds (cheese) Change in temperature ex: water and baking soda feels cool ex: hydrogen peroxide and yeast feels hot Change in color ex: pH indicator going from colorless to color NOT an ex: food coloring in water Light is produced and/or sound is given off Ex: fireworks
Chemical Change indicators Evidence of a chemical reaction Difficult or impossible to reverse Formation of gas Formation of precipitate Change in color Change in energy Endothermic Absorbs heat energy (gets cold) Exothermic Releases heat energy (gets hot) Alka-Seltzer: (Baking soda or sodium bicarbonate) NaHCO3 + Citric acid ---> CO2 + H2O + Sodium Citrate
Evidence of Chemical Change
Energy Release A chemical reaction often releases forms of energy such as light and heat. Glow sticks work when a capsule of phenyl oxalate is broken (by you) and it mixes with hydrogen peroxide. This releases energy that causes a colored dye to glow with light. When you burn something, the fuel is reacting with oxygen in the air to produce fire–a combination of heat AND light.
Forms bubbles or gas Well, back to vinegar and baking soda…the huge release of gas is a good sign that a new substance (the gas, duh) has been produced. Hydrochloric acid creates hydrogen gas when reacting with zinc metal.
color A permanent, unexpected change in color often lets you know that a substance has been chemically, not physically, changed into a new substance. mmm…the perfect cookies Whoa! The total change in color to “char black” is a chemical change.
Perfectly good cookies. odors Yes. Here’s another one…imagine what this: …smells like. Probably not the way it smelled 10 minutes before being pulled out of the oven. odor released ex: baking bread creates new gases Perfectly good cookies. RUINED.
They let you know that a chemical change has happened? One Last One… What do the previous four indicators of chemical change have in common? They let you know that a chemical change has happened? Well, yeah, no kidding. BESIDES that?
All Hard to Reverse! Yeah! Imagine trying to stuff the heat and light back into a burning candle. Uh huh…ouch. Or imagine trying to get burned cookies to go back to being brown. Or take it another step. Try to get a nicely baked cookie to “unbake” and turn into cookie dough. gee…how?
Irreversibility difficult to reverse ex: can’t turn a cookie back into dough
Chemical Changes
The OTHER kind of change So…the other kind of changes tend to: Not release heat or light Not release gas or bubbles Not change the color of something permanently Not release new odors Be somewhat reversible You can cut, mash, smash, stretch, flatten, divide, shave, freeze, thaw cookie dough and it’s STILL cookie dough. Those kinds of changes haven’t made new substances. physical Let’s see you put this all together. A ____ change happens when no new substance is made. The opposite kind of change, a ____ change, DOES create a new substance. chemical
Practice, practice, practice I can distinguish between a physical and chemical change.
What kind of change is it if someone... Tears up paper? Physical change Mixes salt and water?
What kind of change is it if someone... Burns paper? Chemical change Evaporates salt water? Physical change
What kind of change is it if someone... Mixes vinegar and baking soda? Chemical change
Quiz time! Which life cycle is most similar to a chemical change? Why? Grasshopper = Eggnymphadult Butterfly = egglarvapupaadult
What type of change is most likely occurring here? Quiz time! What type of change is most likely occurring here? How do you know?
What type of change is most likely occurring here? Quiz time! What type of change is most likely occurring here? How do you know?
What type of change is most likely occurring here? Quiz time What type of change is most likely occurring here? How do you know?
Physical or Chemical Change? Water evaporates from the ocean.
Physical or Chemical Change? The yolk of an egg, which contains sulfur, causes tarnish to form on silver.
Physical or Chemical Change? The ice on a lake melts to become water in the lake.
Physical or Chemical Change? Charcoal in a fire turns to ash after several hours.
Physical or Chemical Change? A pencil is sharpened in a pencil sharpener, leaving behind shavings.
Physical or Chemical Change? A battery makes electricity to turn on a flashlight.
Physical or Chemical Change? A bicycle rusts when left in the rain.
Physical or Chemical Change? A shirt is accidentally torn in the washing machine.
Physical or Chemical Change? A log is split in two by an axe.
Chemical or Physical Change? Cutting paper? Physical
Chemical or Physical Change? Ice melting? Physical
Chemical or Physical Change? Bread toasting? Chemical
Chemical or Physical Change? Rocket fuel burning? Chemical
Chemical or Physical Change? Sawing wood? Physical
Chemical or Physical Change? Metal rusting? Chemical
Chemical or Physical Change? Disappearing puddle? Physical
Chemical or Physical Change? Candle burning? Chemical
Chemical or Physical Change? Dry ice? Physical
Physical or Chemical Change? Painting Wood PHYSICAL
Physical or Chemical Change? Burning Paper CHEMICAL
Physical or Chemical Change? Digestion of food CHEMICAL
Sugar dissolving in water PHYSICAL Physical or Chemical Change? Sugar dissolving in water PHYSICAL
Iron turning red when heated PHYSICAL Physical or Chemical Change? Iron turning red when heated PHYSICAL
Physical or Chemical Change? Evaporation PHYSICAL
A pond freezing in winter PHYSICAL Physical or Chemical Change? A pond freezing in winter PHYSICAL
Physical or Chemical Change? Melting ice PHYSICAL
Physical or Chemical Change? Cutting wire PHYSICAL
Physical or Chemical Change? Painting fingernails PHYSICAL
Physical or Chemical Change? Cutting fabric PHYSICAL
Physical or Chemical Change? Baking muffins CHEMICAL
Physical or Chemical Change? Shattering glass PHYSICAL
Decomposition of old leaves CHEMICAL Physical or Chemical Change? Decomposition of old leaves CHEMICAL
Physical or Chemical Change? Wrinkling a shirt PHYSICAL
Physical or Chemical Change? An old nail rusting CHEMICAL
Concept check Substance A is a yellow liquid and substance B is a blue liquid. The two are mixed and form a green liquid and a white solid. What evidence suggests a chemical change occurred? What other things could you look for to determine if there was a chemical change?
sToP & tHinK - which shows physical change and which shows chemical change? link to change animation #1 link to change animation #2
Physical and Chemical Changes Quiz Number your paper (1-10)
1. A. Physical Change B. Chemical Change Rusting nails
2. A. Physical Change B. Chemical Change Effervescent tablet
3. A. Physical Change B. Chemical Change Cut paper
4. A. Physical Change B. Chemical Change Vinegar and Baking soda
5. A. Physical Change B. Chemical Change Salt and water
6. A. Physical Change B. Chemical Change Broken glass
7. A. Physical Change B. Chemical Change Burning wood
8. A. Physical Change B. Chemical Change Ice melting
9. A. Physical Change B. Chemical Change Removing iron filings from a mixture
10. A. Physical Change B. Chemical Change Boiling water
Check your paper and place in notebook 1. B - Chemical 2. B - Chemical 3. A - Physical 4. B - Chemical 5. A - Physical 6. A - Physical 7. B - Chemical 8. A - Physical 9. A - Physical 10. A - Physical