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!