Properties and Changes of Materials - Irreversible changes (burning, rusting, mixing acid and bicarbonate of soda)
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
An irreversible change is a permanent transformation that cannot be easily undone to get the original materials back. During these changes, new substances are always formed.
Burning (Combustion) is an irreversible change where a fuel reacts with oxygen () from the air to produce heat, light, ash, and gases like carbon dioxide () and water vapor ().
Rusting is a slow irreversible change that occurs when iron () reacts with both oxygen () and water (). The new substance formed is called iron oxide (), which is a reddish-brown flaky solid.
Mixing an acid (like vinegar) with bicarbonate of soda () creates a chemical reaction that produces salt, water (), and carbon dioxide () gas. The fizzing or bubbling is a sign that a new gas is being formed.
Signs of an irreversible change include: a change in color, the production of a gas (bubbles/fizzing), the release of heat or light, and the formation of a completely new material.
📐Formulae
💡Examples
Problem 1:
When you burn a piece of wood, it turns into grey ash. Is this a reversible or irreversible change? Explain using the products formed.
Solution:
This is an irreversible change.
Explanation:
Burning wood is a chemical reaction where the wood reacts with oxygen () to create new substances: ash, carbon dioxide (), and water vapor (). You cannot turn the ash and smoke back into the original piece of wood.
Problem 2:
A student places an iron nail in a jar of water. After a week, the nail is covered in a brownish-orange crust. Identify the process and the chemical name of the new substance.
Solution:
The process is rusting, and the new substance is iron oxide ().
Explanation:
The iron () in the nail reacted with the oxygen () dissolved in the water () to form a new material. This is irreversible because the rust cannot be turned back into shiny iron through simple physical means.
Problem 3:
What happens to the temperature and state of matter when vinegar is mixed with bicarbonate of soda ()?
Solution:
The mixture fizzes (releases gas) and the temperature usually drops slightly.
Explanation:
When the acid (vinegar) and the base (bicarbonate of soda) react, they produce carbon dioxide () gas, which causes the bubbling. This production of gas and the formation of new substances (sodium acetate and water) indicate an irreversible chemical change.