chemical and physical change

1 ANSWERS

1. salim
   

   Physical Change:
   A physical change in a substance doesn't change what the substance is. For example, if a piece of paper is cut up into small pieces it still is paper. This would be a physical change in the shape and size of the paper,
   
   Chemical Change:
   In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed.For example if the same piece of paper is burned, it is broken up into different substances that are not paper.
   
   Properties of Physical and Chemical Changes:
   Physical changes can be reversed, chemical changes cannot be reversed with the substance changed back without extraordinary means, if at all. When heat is given off in a chemical change or reaction, it is called an exothermic reaction. When heat is absorbed in a chemical change or reaction, it is called an endothermic reaction. The speed at which chemical reactions take place depend on the temperature pressure and how concentrated the substances involved in the chemical reaction are. Sometimes substances called catalysts are used to speed up or help along a chemical reaction. Light is helpful in the processing of film.
   
   Some more Examples:
   A cup of water can be frozen when cooled and then can be returned to a liquid form when heated.
   
   If one decided to mix sugar into water to make sugar water, this would be a physical change as the water could be left out to evaporate and the sugar crystals would remain. However, if one made a recipe for a cake with flour, water, sugar and other ingredients and baked them together, it would take extraordinary means to separate the various ingredients out to their original form.

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