Taking Compounds Apart Chemistry

Learning Goals To be able to explain how compounds come apart To be able to identify gases

Elements cannot be broken down into simpler substances Compounds can be broken down because they are made of two or more elements

Decomposition Refers to a chemical change in which compounds are broken down into simpler substances In general, compounds do not break down by themselves They require energy obtained in one of two ways: Using electricity Adding thermal energy (heat) to the compound

Using Electricity Electrolysis – process during which electricity is used to break down a compound into simpler substances Electrolysis of Water – when electricity is passed through water, some of the water molecules (H2O) break down to form hydrogen gas and oxygen gas

Adding Thermal Energy Decomposition occurs when a match is lit The friction between the match head and the rough strip on the matchbox releases thermal energy This causes chemicals on the match head to break down and catch fire

Baking soda is added to dough and cake batter because heat from the oven causes the baking soda to break down into other chemicals, including carbon dioxide (CO2) bubbles, which cause the bread and cake to rise A catalyst is a substance that speeds up a chemical change without being consumed or chemically changed itself

Gas Tests

Hydrogen gas can be detected using a flaming splint test – a flaming splint will ignite the gas and make a “pop” sound if hydrogen is present Oxygen gas can be detected using a glowing splint test – a glowing splint will reignite if oxygen is present Carbon dioxide gas can be detected using a flaming splint test – a flaming splint will be extinguished if carbon dioxide is present

Success Criteria I CAN explain decomposition I CAN identify the gas present based on a test

To Do… Late work (Element poster, Bohr diagrams) Worksheet Prepare for Quiz (tomorrow)