Physical and Chemical Changes Obtained and modified from: http://mysite.verizon.net/vze4gq6z/sitebuildercontent/sitebuilderfiles/physicalchemicalchangesppt.ppt
What kind of changes does matter undergo? All matter, regardless of state, undergoes physical and chemical changes. These changes can be microscopic or macroscopic.
Physical and chemical properties may be intensive or extensive. Intensive and Extensive Properties
Intensive properties such as density, color, and boiling point do not depend on the size of the sample of matter and can be used to identify substances. What are intensive properties?
Extensive properties such as mass and volume do depend on the quantity of the sample. What are extensive properties?
Physical properties are those that we can determine without changing the identity of the substance we are studying. How can we identify physical properties?
The physical properties of sodium metal can be observed or measured. It is a soft, lustrous, silver-colored metal with a relatively low melting point and low density. • Hardness, color, melting point and density are all physical properties. Examples of physical properties:
What is a physical change? A physical change occurs when the substance changes state but does not change its chemical composition. For example: water freezing into ice, cutting a piece of wood into smaller pieces, etc. The form or appearance has changed, but the properties of that substance are the same (i.e. it has the same melting point, boiling point, chemical composition, etc.)
A chemical property must describe how some substance REACTS or DOES NOT REACT with other substances. • In other words, they describe how a substance will be changed or will not be changed when it interacts with other substances. CHEMICAL PROPERTIES
Characteristics of Physical Changes • Density • Electrical conductivity • Solubility • Adsorption to a surface • Hardness • Melting point • Boiling point • Vapor pressure • Color • State of matter
States of Matter • Density of Matter Two Important Physical Properties
States of Matter (And how the Kinetic Molecular Theory affects each) • Solids • Liquids • Gases • Plasma
Solids • Have a definite shape • Have a definite volume Kinetic Molecular Theory Molecules are held close together and there is very little movement between them.
Liquids • Have an indefinite shape • Have a definite volume Kinetic Molecular Theory: Atoms and molecules have more space between them than a solid does, but less than a gas (ie. It is more “fluid”.)
Gases • Have an indefinite shape • Have an indefinite volume Kinetic Molecular Theory: Molecules are moving in random patterns with varying amounts of distance between the particles.
Kinetic Molecular Model of Water At 100°C, water becomes water vapor, a gas. Molecules can move randomly over large distances. Between 0°C and 100 °C, water is a liquid. In the liquid state, water molecules are close together, but can move about freely. Below 0°C, water solidifies to become ice. In the solid state, water molecules are held together in a rigid structure.
On earth we live upon an island of "ordinary" matter. The different states of matter generally found on earth are solid, liquid, and gas. We have learned to work, play, and rest using these familiar states of matter. Sir William Crookes, an English physicist, identified a fourth state of matter, now called plasma, in 1879.
Plasma Plasma is by far the most common form of matter. Plasma in the stars and in the tenuous space between them makes up over 99% of the visible universe and perhaps most of that which is not visible.
EXAMPLES: • Computer chips and integrated circuits • Computer hard drives • Electronics • Machine tools • Medical implants and prosthetics • Audio and video tapes • Aircraft and automobile engine parts • Printing on plastic food containers • Energy-efficient window coatings • High-efficiency window coatings • Safe drinking water • Voice and data communications components • Anti-scratch and anti-glare coatings on eyeglasses and other optics
Density = mass (g) D = g or g volume (ml) ml cm3 • Note ml = cm3 m Density v D
Osmium is a very dense metal. What is its density in g/cm3 if 50.00 g of the metal occupies a volume of 2.22cm3? 1) 2.25 g/cm3 2) 22.5 g/cm3 3) 111 g/cm3 Learning Check D1 lecturePLUS Timberlake
2) Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass = 50.00 g = volume 2.22 cm3 = 22.522522 g/cm3 = 22.5 g/cm3 Solution lecturePLUS Timberlake
A solid displaces a matching volume of water when the solid is placed in water. 33 mL 25 mL Volume Displacement lecturePLUS Timberlake
What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL? 1) 0.2 g/ cm3 2) 6 g/m3 3) 252 g/cm3 33 mL 25 mL Learning Check lecturePLUS Timberlake
2) 6 g/cm3 Volume (mL) of water displaced = 33 mL - 25 mL = 8 mL Volume of metal (cm3) = 8 mL x 1 cm3 = 8 cm3 1 mL Density of metal = mass = 48 g = 6 g/cm3 volume 8 cm3 Solution lecturePLUS Timberlake
Which diagram represents the liquid layers in the cylinder? (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL) 1) 2) 3) K W V Learning Check3 V K W W V K lecturePLUS Timberlake
(K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL) 1) V Solution W K lecturePLUS Timberlake
What are chemical changes? A chemical change occurs when a substance changes into something new. This occurs due to heating, chemical reaction, etc. You can tell a chemical change has occurred if the density, melting point or freezing point of the original substance changes. Many common signs of a chemical change can be seen (change in color, change in temperature, formation of a gas, emission of light, formation of a precipitate).
Characteristics of Chemical Changes • Ability to act as reducing agent • Reaction with other elements • Decomposition into simpler substances • Corrosion • Reaction with acids • Reaction with bases (alkalis) • Reaction with oxygen (combustion) • Ability to act as oxidizing agent
Chemical properties describe the way a substance can change or react to form other substances. These properties, then, must be determined using a process that changes the identity of the substance of interest. What are chemical properties?
One of the chemical properties of alkali metals such as sodium and potassium is that they react with water. To determine this, we would have to combine an alkali metal with water and observe what happens. • In other words, we have to define chemical properties of a substance by the chemical changes it undergoes. How can chemical properties be identified?
Bubbles of gas appear • A precipitate forms • A color change occurs • The temperature changes • Light is emitted Evidence of Chemical Change
Comparison of Physical and Chemical Properties Create a Venn diagram to compare and contrast physical and chemical properties