GLOSSARY - Hydrogen Fuel - page 41

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acid rain: Rain, snow, fog, or
mist that contains acid substances
and damages the environment.
algae: Life forms that resemble
plants and that usually grow
in water.
alloy: A mixture of two or more
metals.
atmosphere: The envelope of air
that surrounds the planet.
atom: The smallest part of an
element that has the properties of
that element.
biomass: Plants and animal
wastes that can be used as fuel.
carbon dioxide: A gas formed
when fossil fuels are burned; also
written as CO 2 .
catalyst: A substance that speeds
up a chemical reaction.
chemical reaction: A process
that changes the molecules of
substances by moving atoms
around.
circuit: A path followed by an
electrical current.
compound: A substance that
is formed when two or more
elements unite.
device: Something that does
some action.
electrode: A terminal where an
electric current l ows in or out.

electrolysis: The use of an
electric current to break down
a chemical compound into its
components.
electrolyte: A solution of
chemicals that conducts
electricity.
electron: A small, negatively
charged particle in an atom.
element: A basic chemical
substance that cannot be divided
into simpler substances.
fossil fuels: Fuels, such as coal,
natural gas, or oil, that were
formed underground over millions
of years from the remains of
prehistoric plants and animals.
Such fuels are not renewable.
fuel cell: A device that uses a
reaction between two substances,
such as hydrogen and oxygen, to
make electricity.
gasii cation: The process of
changing a liquid or solid into a
gas.
global warming: The gradual
warming of Earth's atmosphere
and surface, caused by the
buildup of carbon dioxide and
other greenhouse gases that trap
heat.
hydrogen fuel: Fuel that uses
hydrogen gas or liquid as an
energy carrier.