Chemical Reactions and Equations

Physical Changes: a change of state and do not create a new substance. Ice melting to water, to dry ice subliming to produce fog are physical changes.

 Chemical changes: a reaction where one or more substances is transformed into one or more new products.
They are can be identified by observing:
* A substance 'disapears'
* A gas is given off (effervescence)
* A solid is precipitated
* A colour change occurs
* A new odour is released
* Light is given off

 Chemical Equations - used to represent a chemical reaction, showing reactants and products and their physical states. Catalysts and other agents can also be shown above the arrow between sides.

 Reactants ----> Products
To Write a Chemical Equation: A General Guide

1. Write out reactants on the left and products on the right, often obtained from information given in a question, including states.

2. Change the little numbers at the bottom to balance the charges of each compound

3. Balance equation to satisfy law of conservation of mass - each element must have the same number of atoms on either side of the reaction.


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