Chemical Reactions

In general:

Reactants ---------> Products

For example:

For the thermal decomposition of zinc carbonate, the reactant is zinc carbonate and the products are zinc oxide and carbon dioxide.

The word equation is:

Zinc Carbonate -----> Zinc Oxide + Carbon Dioxide

*Substances are made up of atoms which are the smallest part of an element that can take part in chemical reactions. 

* A compound consists of atoms of two or more different elements chemically joined.

The chemical formula of a compound shows symbols of the element it contains and ratios in which the atoms *are present

Balanced equations shows what happens to atoms in a chemical reaction:

Zinc Carbonate -----> Zinc Oxide + Carbon Dioxide

ZnCO³(s) --------> ZnO(s) + CO²(g)

*There are the same numbers of atoms of each element on both sides, so it's a balanced equation.

*(s) and (g) are state symbols showing what is a solid and a gas. 

*Liquids are shown by (l) and aqueous solutions shown by (aq).

Atoms aren't made or destroyed in a chemical reaction but rearranged meaning the total mass stays the same before and after the reaction.

Precipitation reactions happen when soluble substances react together to form a insoluble product, namely the precipitate. 

Silver Nitrate and Potassium Bromide react together to form insoluble silver bromide.

Silver Nitrate + Potassium Bromide ------> Potassium Nitrate + Silver Bromide

AgNO³(aq) + KBr(aq) ------> KNO³(aq) + AgBr(s)

Key Words:

Reactant

Products

Atom

Element

Compound

Chemical Formula

State Symbols

Precipitation Reactions

Soluble

Insoluble

Precipitate

Questions:

1) What is an atom?

2) What does the ³ in a formula tell you?

3) How do precipitation reactions occur?

What you should know:

• 2.12 Be able to describe the ease of thermal decomposition of different metal carbonates.
• 2.13 You should understand that:
  • a) atoms are the smallest particles of an element that can take part in chemical reactions
  • b) during chemical reactions, atoms are neither created nor destroyed
  • c) during chemical reactions, atoms are rearranged to make new products with different properties from the reactants 
  • 2.16 You should know and understand that the total mass before and after a reaction in a sealed container is unchanged, as shown practically by a precipitation reaction (known as the 'Law of Conservation of Mass').