ZIMSEC O Level Combined Science Notes: Chemical Reactions

Introduction to reactions

  • A compound is formed when a chemical reaction takes place
  • Chemical change takes place to form the compound
  • Word equations can be used as a short hand way to show what has happened
  • An example of a chemical equation is:
  • \text{iron + sulpher}\rightarrow \text{iron sulphide}
  • As already stated a mixture is made by a physical (as opposed to chemical) change
  • Iron and sulpher are elements
  • Iron is made up entirely of iron atoms
  • Sulpher is made up entirely of sulpher atoms
  • These two elements can be combined in a chemical reaction to form a new substance called a compound
  • These two have to be heated first before they can combine to form iron sulphide
  • The heat is required to start the reaction for once it starts it gives out heat
  • The mixture glows red as it reacts even if the burner is removed
  • Iron and sulpher combine at a molecular level
  • This is done when iron atoms form bonds with sulpher atoms
  • These bonds can be broken by chemical means to obtain sulpher and iron again
  • Since iron and sulpher are elements they cannot be further broken down
  • Iron and sulpher are thus the simplest substances (elements) that can be obtained if iron sulphide is broken down
  • Chemical reactions always result in the formation of new substances
  • Some reactions require heat in order to start/take place

Chemical reactions and Oxides

  • Oxygen is an that is found in the atmosphere
  • When elements burn up in air they combine with oxygen to form new compounds
  • These compounds are known asĀ oxides
  • Oxides-are compounds formed when elements combine with oxygen
  • For example carbon in firewood combines with oxygen when it is burnt to form carbon dioxide
  • And sometimes carbon monoxide

To access more topics go to the Combined Science Notes page.

Quick NetOne, Telecel, Africom, And Econet Airtime Recharge

If anything goes wrong, chat with us using the chat feature at the bottom right of this screen