Y7 Chemical Reactions Topic words

Irreversible

Permanent change which cannot be reversed

Carbon dioxide test

A gas which turns limewater cloudy

Product

A substance formed from a chemical reaction

Oxide

A compound which includes oxygen

Word equation

A way of writing out what happens in a chemical equation

Combustion

The scientific word for burning

Carbonate

A particle which contains carbon and oxygen

Test for hydrogen

A gas which makes a squeaky pop when a lit splint is placed near it

Test for oxygen

Relights a glowing wooden splint

Physical change

A change in which no new substances are formed

Reversible

A reaction where the products can easily be returned to their starting form

Limewater

A chemical which goes cloudy when carbon dioxide is bubbled through it

Rust

Substance formed when iron or steel reacts with oxygen and water

Chemical change

A change which produces a new substance

Universal indicator

A pH indicator with colour changes over a pH range from 0 (alkali) to 14 (acid). pH 7 is neutral

Metals + oxygen

Metals react with oxygen to produce metal oxides

Acid Rain

Sulfur dioxide and nitrogen oxides are responsible for acid rain. It is harmful to the environment by changing the pH of lakes, rivers and soil.

How do we know that a chemical reaction has taken place?

Change in temperature; change in colour, fizzing (effervescence)

Conservation of mass

During any chemical reaction no particles are created or destroyed. Instead the atoms are rearranged from the reactants to the products. Mass is never lost or gained in chemical reactions

Properties of metals

Shiny, good conductor of heat and electricity, sonorous, high density (feel heavy for their size), strong, malleable, generally solid at room temperature

Properties of non metals

Dull, about half are solids and about half are gases, one (bromine) is a liquid, low density (feel light for their size), weak, brittle, poor conductor of heat and electricity, non sonorous.

Alkalis

Bases are substances that have a pH of more than 7. When bases are dissolved in water, they are known as alkalis.

Acid

Substances with a pH of less than 7 are acids. The stronger the acid, the lower the pH number. Acids turn blue litmus paper red. They turn universal indicator red if they are strong, and orange or yellow if they are weak.

reactant

the substances that are put together to react in a chemical reaction

precipitate

A solid that forms from a solution during a chemical reaction.

oxygen test

Relights a glowing splint

neutralisation reaction

The reaction of an acid and a base forming a salt and water to bring the pH to neutral.

neutral pH

pH of 7

Examples of useful neutralisation reactions

toothpaste, indigestion (antacid) tablets, treating soil that is too acidic/alkaline.