7.5: Taking Compounds Apart
pg. 256
Decomposition of Compounds
Decomposition: is the breaking down of a compound into
simpler substances.
When compounds are broken down into simpler substances,
it is a chemical reaction called decomposition. Compounds
don not usually break down on their own, they need some
help, usually an input of energy. Energy is added in two
ways:
- Using electricity.
- Adding thermal energy to the compound.
Electrolysis
Electrolytes: is the process by which electricity is used to
break down a compound into simpler substances.
Electricity that is used to breakdown compounds is known
as electrolysis. In the previous lab, electrolysis was used to
decompose water into hydrogen gas, (H2) and oxygen gas,
(O2). The observation from the lab, supported the
composition of water. For every oxygen atom there were
two hydrogen atoms, chemical formula of water is H2O.
When the gases were produced one test tube had twice as
much gas as the other test tube. The test tube with twice as
much gas was determined by a gas test to be hydrogen, and
the other was oxygen.
Refining Aluminum
Most metals on the periodic table are not found as elements
in nature, but as compounds. To separate these metals,
electrolysis is used. The minerals similar to aluminum
oxide are common in nature. Pure aluminum is extracted by
passing electricity through liquid aluminum oxide, (Al2O3),
causing aluminum to separate from oxygen.
Heating and Decomposition
Heating compounds caused them to breakdown or
decompose.
e.g.: Lighting a match or baking a cake.
Decomposition of Hydrogen Peroxide.
Catalyst: is a substance that speeds up a chemical change
without being consumed or chemically changed itself.
Hydrogen peroxide (H2O2) breaks down at room
temperature, 20oC. The process of decomposition can occur
faster when assisted by a catalyst. The catalyst will speed
up the chemical reaction without being used within the
chemical reaction.
Hydrogen peroxide is a toxic substance that can be used to
kill bacteria and disinfecting cuts.
Check Your Learning:
Questions 1 – 5, pg. 259
Wrap Up:
- Compounds can break down, or decompose, into simpler
substances.
- Energy is needed to decompose a compound. Common
sources of energy are heating and electricity.
- Some substances can speed up chemical changes without
being used up. These substances are known as catalyst.