1 / 7

Physical and chemical reactions

Physical and chemical reactions. Compare physical & chemical changes and recognise signs of a chemical reaction. How do you know if a reaction is a physical one?. Is it reversible? Yes: then it is a physical reaction Does a new substance appear? If no, then it is a physical reaction

ozzy
Download Presentation

Physical and chemical reactions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Physical and chemical reactions Compare physical & chemical changes and recognise signs of a chemical reaction

  2. How do you know if a reaction is a physical one? • Is it reversible? Yes: then it is a physical reaction • Does a new substance appear? If no, then it is a physical reaction • Does a substance disappear? If it has just melted then it is a physical reaction • Has there been an energy change? Has it got hotter or colder? If no then it is a physical reaction

  3. Simple examples of physical changes: • Ice melting: this is a change in state and is a common physical change. • All changes in state are physical reactions. • Sugar dissolving: this is a physical reaction as it can be reversed. The water just needs to be evaporated off. • When a substance is dissolved, it can be undissolved by removing the water through evaporation • Movie • Bending a nail: this can be easily reversed by unbending it • A change in shape is just a physical reaction.

  4. How do you know a reaction is a chemical reaction? • Is the reaction reversible? If no then it is a chemical reaction • Does a new substance appear? If yes, then it is a chemical reaction • Does a substance disappear? Has it dissolved? Then it is a chemical reaction, if it has just melted then it is a physical reaction • Has there been an energy change? Has it got hotter or colder? If yes then it is a chemical reaction

  5. Examples of chemical reactions • Baking a cake: this can’t be reversed, you can’t unbake a cake. • Baking soda reacting with vinegar: a gas is given off, this is a new substance • movie • When the baking soda reacts with the vinegar it disappears: it is reacting. • When some chemicals are mixed there is a change in temperature: think about an instant ice pack: the chemicals are mixed and it gets very cold.

  6. Basic experiments: • Aim: to observe a candle burning and decide where chemical and physical reactions are occuring • Method: • Light a candle • Write down your observations • Label a candle diagram showing what chemical and physical reactions are occuring

  7. Results: • Observations: … • Conclusion: both chemical and physical reactions occur when a candle burns physical chemical physical chemical

More Related