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Substances Mixtures
Substances Mixtures
Elements Compounds Homo-geneous
Hetero-geneous
Conservation of MassUnit 1: Measurement & Matter
Key Question What are four possible clues that a
chemical change (or reaction) has taken place?
Transfer of energy Change in color (be careful with this one) Production of a gas (e.g. H2, O2, CO2) Formation of precipitate (ppt)
Is this a reaction? Antacid Tablet…
Gas is produced
Is this a reaction? Adding food coloring to water
This is not a reaction although a color change is observed
A new substance is not created The substances can be
physically separated Distillation Evaporation
Is this a reaction? Burning a log
Transfer of energy (chemical to thermal) Change in color (brown to black/gray) Production of gas (CO2 and H2O)
Key Question How are the mass of the reactions and
the mass of the products of a chemical reaction related?
During any chemical reaction, the mass of the products is always equal to the mass of the reactants.
Law of Conservation of Mass Mass is neither created nor destroyed
Mass of reactants = mass of products
So…. Burning a log?
After a log burns, what is left? ASHES
If the Law of Conservation of Mass is true, where does the mass of the log go?
Combustion Reaction
The mass of the wood and oxygen is converted to carbon dioxide gas and water vapor.
The gases escape into the atmosphere!
C6H12O6 + 6 O2 6 CO2 + 6 H2OWood + oxygen carbon dioxide +
water
Practice (Conservation of Mass)
Sodium + Chlorine Sodium Chloride
If 50 grams of sodium react with chlorine to form 126 grams of salt. How many grams of chlorine reacted?
50 g 126 g76 g
Practice (Conservation of Mass)
Water Hydrogen Gas + Oxygen Gas
If 178.8 g of water is separated into hydrogen and oxygen gas, and the hydrogen gas has a mass of 20.0 g, what is the mass of the oxygen gas produced?
178.8g 20.0 g 158.8 g
Homework
Elements Quiz TOMORROW Wed. 9/24!