Chemical reactions

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reactants products

A chemical reaction is a change that takes place when one or more substances

(called reactants) form one or more new substances (called products).

Bonding and electrons

• When elements react, their atoms join with other atoms to form molecules and/or compounds. This is Bonding.

• Bonding involves giving, taking or sharing electrons to form ions or molecules

Metals bonding with Non-metals

• Compounds formed from metals and non metals consist of ions. • Metals lose electrons to form positive ions. • Non metals gain electrons to form negative ions

Word and symbol equations

• Chemical reactions can be represented by word equations or by symbol equations

• No atoms are lost or made during a chemical reaction so the mass of products equals the mass of the reactants

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Symbol equation:

C(s) + O2(g) CO2(g)

carbon carbon dioxideoxygen+

Word equation:

HT candidates should be able to balance symbol equations

A symbol equation must be balanced to give the correct ratio

of reactants and products.

Limestone = calcium carbonate

• Limestone is mainly composed of the compound calcium carbonate (CaCO3)

• Limestone is quarried (dug up) and can be used as a building material

Heating calcium carbonate

• Calcium carbonate can be decomposed by heating (thermal decomposition) to make calcium oxide and carbon dioxide

• The carbonates of magnesium, copper, zinc, calcium and sodium decompose on heating in a similar way

Limestone cycle

Limestone and its products can be involved in various useful chemical reactions:

Summary of limestone chemistry

calcium oxide water calcium hydroxide+

calcium carbonate

calcium oxide

carbon dioxide +

thermal decomposition of limestone

production of calcium hydroxide

using limewater to test for carbon dioxide.

calcium carbonatecalcium hydroxide

(aq)

carbon dioxide ++ water

Making building materials

Limestone is heated with clay to make cement. Cement is mixed with sand to make mortar and

with sand and aggregates to make concrete

Limestone + Clay Cement

Cement + Sand Mortar

Cement + Sand and aggregates

Concrete

Carbonates and acid

Carbonates react with acids to produce carbon dioxide. Limestone is damaged by

acid rain

Pros and cons of quarrying