Chemical vs physical properties
Elements and compounds can be described by their chemical and physical properties
Physical property: characteristic of a substance you can observe (using your senses) without changing it into something else
• State of matter (solid, liquid, gas)• Melting, freezing, boiling point• Magnetism• Density• Color• Shape• Malleability• Solubility• Specific heat
Chemical properties: properties of an element or compound in a chemical reaction
• pH• Reactivity• Flammability/Combustion• Rusting• Bond
Practice on Identifying Chemical and Physical Properties1. Water boils at 100 degrees Celsius. 2. Diamonds are capable of cutting glass. 3. Water can be separated by electrolysis into hydrogen and
oxygen. 4. Sugar is capable of dissolving in water. 5. Vinegar will react with baking soda. 6. Yeast acts on sugar to form carbon dioxide and ethanol. 7. Wood is flammable. 8. Aluminum has a low density. 9. Ammonia is a gas at room temperature. 10.Bromine has a red color.
Which of the following conclusions can be drawn from the information shown?
a. Most types of matter heat up at the same rateb. Most types of matter cool at the same ratec. It takes less energy to heat 1g of silver than 1g of goldd. It takes more energy to heat 1g of water than 1g of copper
Material Specific Heat
Aluminum 0.899
Copper 0.387
Gold 0.129
Silver 0.234
Water 4.182
Wood 0.176
Magnesium melts at 650°C. If a 100g sample of magnesium melts at 650°C, then a 75g sample would melt at:
a) 325°Cb) 650°Cc) 487.5°Cd) 162.5°C
Chemical change: atoms are rearranged, I have different substances at the end of a chemical reaction/change
• Change in color• Formation of precipitate (L+LS)• Formation of a gas• Creation of light• Burning• Change in temperature (exothermic,
endothermic)
Changes can be physical or chemical
Physical changes do not rearrange atoms, I have the same substance I started with. I can reverse a physical change
Change in shapeChange in phaseDissolving
Reversable
Practice on Identifying Chemical and Physical Changes
1.Dry ice, solid carbon dioxide, is sublimed at room temperature.
2.Salt is dissolved in water. 3. Iron rusts in a damp environment. 4.Gasoline burns in the presence of oxygen. 5.Hydrogen peroxide decomposes to water and
oxygen.
Combustion: reacting with oxygenfrequently producting CO2& water
C3OH + O2 CO2 + H2O + heat
2Mg + O2 2MgO + Heat
______________________________________2H2 + O2 2H2O + heat
NH4 + NO2 N2O + H2O
Compounds or molecules are represented using a chemical formula
4CO₂Subscripts (little number) tell you the
number of atoms in the 1 molecule of the compound
Coefficients (big number out front) tell you how many molecules
(no number means the number is 1!)
Calculate the number of atoms of each element
AgMnO4
AlBO2
CH3OH
BaSi2O5
Calculate the total number of atoms of each element
2AgMnO4
6AlBO2
7CH3OH
2BaSi2O5
KNO3
Conservation of Mass
Mass on the reactant side of the equation equals the mass on the product side of the equation
Number and type of atoms on the reactant side of the equation equals the number and type of atoms on the product side of the equation.
Reactants Products
To check for balance, multiply coefficient x subscript
__H₂ + __O₂ __H₂OA. 1, 1, 1B. 2, 1, 2C. 2, 1, 2 D. 2, 2, 2
__K + __B2O3 __K2O + __BA. 3, 2, 3, 2B. 6, 1, 3, 2C. 6, 2, 3, 2D. 3, 2, 2, 2
To balance an equation its cool to change coefficients, do not change subscripts….don’t mess w/the little people (you’ll change the molecule’s identity!)
1. Calculate the mass of the product of 6.40 g of magnesium with 1.32 g of oxygen .
2. Calculate the mass of the zinc that reacts with 4.11 g of hydrochloric acid to form 9.1 g of zinc chloride and 3.97 g of hydrogen gas.
3. During the combustion of 5.00 g of Butane in the presence of oxygen, 4.01 g of carbon dioxide and 3.55 g of water is given off. How much oxygen was needed to totally combust the butane?
Review…..
• Made when two or more elements combine during a chemical reaction
• Examples:• Water• Salt• Sugar
• Chemical Change
Compound:
What is evidence that a chemical reaction is happening again?
• Fire, Combustion, Explosion
• A new color appears/disappears
• Temperature change• Production of Gas, gas
bubbles• Production of
Precipitates
Compounds are formed or separated through chemical reactions…
• Combines 2 or more substances without producing a chemical reaction
• NOT the same throughout - heterogeneous
• Can be separated easily
• Examples:• Soil • Fruit salad
• Physical Change
Mixture
• A type of MIXTURE that IS the same throughout - homogenous
• Solute- substance being dissolved• Solvent- substance doing the dissolving
• Examples:• Salt water • Lemonade
• Physical Change
Solution:
Salt = Solute
Water= Solvent
Salt Water= Solution