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Properties
Physical property:
Can be observed without changing the identity (formula) of a substance
Chemical Property:
Can ONLY be observed when the identity (formula) of a substance is changed
Changes
Physical Change: Can be observed without changing the identity (formula) of a substance
Chemical Change:Can ONLY be observed when the
identity (formula) of a substance is changed
Involves a chemical reaction
Chemical change is a chemical reaction
Reactants: Starting substances
Products: Final (new) substances
Reactants → Products
Physical or Chemical Property?
• Iron Rusts
• Iron Melts (at high temperature)
• Sugar dissolves in water
• Alka-Seltzer fizzes when you add it to water
Physical Separation Methods
• Distillation: – Separates substances by differences in their boiling
points (usually liquids)
• Filtration:– Separates solid from liquid
• Chromatography: – Separates substances by differences in how they are
absorbed by a stationary phase and a mobile phase. (Ex: liquid mobile phase and paper stationary phase)
Physical Separation Techniques
Each method separates on the basis of a physical property
Distillation
Sorting
Filtration
Evaporation
Separation of a Mixture
How would you separate a mixture of
Salt and Sand
into its separate components?
What do you need to know?
Properties of saltWhite solidDoes not melt (until it reaches HIGH temp)Dissolves in water
Properties of sandSolid (color varies)Does not meltDoes not dissolve in water
Possible Method
Add mixture to waterDissolve saltFilter out sand
Salt left in waterEvaporate off water
Mixture 2:
Salt, sand and iron filings
How would you separate this mixture into its separate components?
Physical Properties—Changes of State
Heat must be added
Melting Solid to Liquid
Evaporation or
Vaporization
Liquid to Gas
Sublimation Solid to Gas directly—
Skip Liquid state
Physical Properties—Changes of State
Heat must be removed
Freezing or Fusion
Liquid to Solid
Condensation Gas to Liquid
Deposition Gas to Solid directly—
Skip Liquid state
Energy
Energy is ability to do work (cause change)
Potential energy—stored energy
(Boulder on top of hill)
Kinetic energy—energy in use (motion)
(Boulder rolling down hill)
Intensive Properties:
Independent of amount of substance
boiling point, density, color
Extensive properties:
Depend on amount of substance
mass, volume
Can We Explain and Predict Physical and Chemical Properties
of Matter?
Properties are related to the structure of matter
Need to examine pure substances in order to determine what the properties of a substance are
Element
Cannot be broken down into simplersubstances by chemical means.
Contains only one kind of atom
Smallest unit is atom
Represented by atomic symbol (one or two letters)
http://www.privatehand.com/flash/elements.html
Approximately 116 elements known
Most are solids. Some are gases. Only two (Br and Hg) are liquids.
Most elements are metals (are shiny, conduct electricity)
A few elements are nonmetals (including the gaseous elements)
• Seven gaseous elements exist as diatomic molecules (two atoms)
H2 O2 N2 F2 Cl2 Br2 I2
The subscript “2” indicates that there are two atoms of the element
Compounds
Can be broken down into simpler substances (elements) by chemical means
Contains two or more kinds of atoms (elements) combined in definite ratio
Atoms are held together by bonds between atoms
Smallest unit is molecule
Represented by formula
Chemical Formula
Chemical formula uses atomic symbols to show what elements and how many atoms of each element are in the compound
The number of each type of atom is shown by using a subscript after the symbol
If there is no subscript, we assume it is “1”
Examples
H2O 2 H atoms 1 O atom
CO 1 C atom 1 O atom
CO2 1 C atom 2 O atoms
Extra O makes a big difference
CO kills quickly. CO2 made by body.
Types of formulas
Molecular Formula gives the number and type of atoms in molecule
Structural Formula gives number and type of atoms in molecule AND shows how they are connected
Must “balance” equation so that there are the same number of atoms of each kind on both sides of the equation
2 CO + O2 → 2 CO2
RULE: Cannot change the formula of substance---can only change the number of molecules
Coefficients
The numbers in front of a formula show the number of molecules of the substance
2 CO + O2 → 2 CO2
2 CO = 2 molecules of CO
Practice Balancing Equations
• AgNO3 + HCl AgCl + HNO3
• HCl + O2 H2O + Cl2
• Ba(OH)2 + HCl BaCl2 + H2O
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