Types of reaction

If an acid reacts with a base, it can from a netural solution containing a salt.

Acid+ Base   salt+water

Acid+ metal   salt + hydrogen

Exothermic-Heat out- gets HOT

Endothermic-Heat in- gets cold

When some solutions are mixed, they react & give a product which is insoluble(it doesn't dissolve). It appears as tiny, solid bitd called a percipitate. E.g

Sliver nitrate+ Sodium Chloride - Sliver Chloride + Sodium Nitrate

     (soluble)       (soluble)                (insoluble)        (soluble)

When hydrogen gas is passed over hot copper oxide, this reaction takes place ( symbols have also been used so that you can see what is happening to the atoms)

Copper Oxide+Hydrogen- Copper+water

CuO             +H2              - Cu     + H2O

This is an example of a redox reaction: Copper oxide has lost oxygen it has been reduced. 

Hydrogen has ganied oxygen: it has been oxidized

Reduction and oxidation always happen together, which is why the name redox is used.                          

One substance pushes out another and takes its place. For example, if an iron nail is placed in copper sulphate solution, some dissolves and displaces in the solution. The copper is deposited on the nail as a brown coating:

Iron+ Copper Sulphate - copper + Iron sulphate

There is a displacement reaction whenever a metal reacts with an acid. The metal displaces hydrogen in the solution. (Remember: all acids cotain hydrogen) 

A substance splits to from simpler substances. For example, if calcium carbonate is heated to 1100C, itb splits to from calcium oxide & carbon dioxide