Week 4-How much gas can be produced by a non-reversible change?  (Copy)

During our marvellous mixtures topic, all the changes which we discussed were reversible. This means that they can be separated again.

A change is called irreversible if it cannot be changed back again. For example you cannot change a cake back into its ingredients again.

Irreversible changes are permanent. They cannot be undone. This topic deals with these changes where a chemical reaction takes place.

In an irreversible change, new materials are always formed. Sometimes these new materials are useful to us.

Please watch the video clip below to understand the difference between a chemical change and a physical change.


Heating

Heating can cause an irreversible change. For example you heat a raw egg to cook it. The cooked egg cannot be changed back to a raw egg again.

When you cook a egg the change is irreversible

This is what happens when we cook our food. Watch this clip about the chemistry involved in cooking:www.bbc.co.uk/education/clips/z9wkjxs

Chemical reactions are irreversible changes:

Mixing substances can cause an irreversible change. For example, when vinegar and bicarbonate of soda are mixed, the mixture changes and lots of bubbles of carbon dioxide are made. These bubbles, and the liquid mixture left behind, cannot be turned back into vinegar and bicarbonate of soda again.

 The vinegar and bicarbonate of soda are the reactants because they are the chemicals we start with. The carbon dioxide and remaining liquid are the products because they are what is produced.

Vinegar plus bicarbonate of soda forms bubbles of carbon dioxide

Task: Please chose which level task you wish to do, either 1* or 3*. You can either print out the sheets or copy the table  and complete it in your book. The answers are there but only use them if you get really stuck please.

Optional extension activities: You could have a go at making a pocket rocket to learn how the products of chemical reactions can be useful. Click here to learn more about pocket rockets: www.bbc.co.uk/bang/handson/fizzbang.shtml


Extra reading: There is an interesting book in the Curriculum Visions science section about this topic. Below is the picture of some of the book. The username is fairfield.leics and the password is LE112AE.