Embedded Files
See the Matariki Google site linked by a button on the Home page
Links to other pages about rates of chemical reactions
Links to other pages about rates of chemical reactions
An introduction to Chemical reactions
An introduction to Chemical reactions
A substance may react when mixed with another substance to form a new substance. When this happens, a chemical reaction has occurred.
The following signs indicate that a chemical reaction is occurring/has occurred:
a temperature change (either heat is given off or the temperature decreases)
light is given off
flames and smoke are observed
bubbling and fizzing of a gas being given off
a smell or odour is observed
a colour change is observed
a brand new substance that is unlike the starting substance(s) is produced. This might include a change in state, such as, two liquids reacting together to make a solid and liquid.
Sometimes there are other indicators, such as, electricity is produced, which can be measured using a voltmeter or multimeter.
In a chemical reaction chemical bonds are broken and new ones are made. We will look at this in more detail later.
For substances to react, their particles must collide. The particles may be atoms, ions or molecules. For a 'successful' collision the particles must have sufficient energy. We will look at this in more detail later.
An Example of a chemical reaction
An Example of a chemical reaction
Your Science teacher might have shown you this chemical reaction in class. In the reaction between hydrogen gas and oxygen gas (when a balloon containing hydrogen is ignited), a new product, water, is formed.
If you haven't seen this demonstration in class then watch the video below:
In the reaction above:
hydrogen gas exists as hydrogen molecules, two hydrogen atoms bonded together.
oxygen gas exists as oxygen molecules, two oxygen atoms bonded together.
When the two gases are mixed (when the hydrogen balloon is ignited) the oxygen and hydrogen molecules collide and the bonds holding the atoms together are broken.
New bonds form between oxygen and hydrogen atoms to produce water.
Reactants and Products
Reactants and Products
In a chemical reaction reactants are the original substances. Products are the substances formed. In the example above, hydrogen and oxygen gases are the reactants, and water is the product.
A word equation can be used to describe a reaction. The reactants are put on the left of the arrow, and the products are put on the right of the arrow.
A balanced symbolic equation can also be used the describe a chemical reaction. The big number in front of the formulae give the number of molecules involved. In a balanced equation the number of each type of atom are the same on both sides of the equation.
The drawing below shows the word and symbolic equations for the hydrogen balloon reaction.
Page updated
Report abuse