1. What are some examples you can find to represent physical and chemical changes?
2. Where do we see these changes in our regular, daily lives?
Changes in matter can be categorized into two groups:
1. Physical changes:
When a physical change occurs, no new substance or element is formed. Stays same substance, but may change shape or state (water evaporating, metal bending)
Example: When water is heated, its particles get excited and spread out. It becomes less dense and changes into a gas. It is still H2O, but it is no longer a liquid.
2. Chemical changes:
When a chemical change occurs, a substance and its original properties are changed. The particles stay the same but they are rearranged so that you cannot get the original substance back (without undergoing a new chemical change)
Example: When vinegar and baking soda are mixed (like in the classic Science Fair Volcano experiment), their particles interact and create a foam. They expand and bubble, and the final substance is no longer vinegar OR baking soda. It is something new, and cannot be separated back into vinegar or baking soda.
Indicators are signals that tell us a change has occurred.
Some indicators of Chemical Change can include:
- Colour changes
- By-product is created (a gas, powder, condensation, etc. is released)
- Temperature changes (the reaction becomes hot or cold)
- Odour released
How can you know which change has occurred? (Physical vs. Chemical)
- If two or more of the above indicators occur, then it is likely that a chemical change has taken place.
- You cannot be sure that a chemical change has occurred unless you are certain a new substance has formed.
- You must do careful tests before and after the change to make sure that the final substance is different than the original substance.
Some examples of Physical Properties include:
When Physical Properties change, we say that a Physical Change has occurred.
Some examples of Chemical Properties include:
- Reactivity with other chemicals
- Coordination number
- Enthalpy of formation
- Heat of combustion
- Oxidation states
- Chemical stability
When Chemical Properties change, we say that a Chemical Change has occurred.