 |
In a chemical reaction, new substance(s) are always formed.
A chemical reaction which releases energy (often heat, but can be other forms of energy) is called EXOTHERMIC.
A chemical reaction in which energy is taken in is called ENDOTHERMIC.
Chemical reactions can be shown by:
| COLOUR CHANGE | e.g. copper carbonate changing from green to black (copper oxide) on heating. |
| SOLID FORMED [PRECIPITATE] | e.g. silver chloride formed when silver nitrate and sodium chloride solutions are mixed. |
| GAS GIVEN OFF | e.g. carbon dioxide released when calcium carbonate reacts with hydrochloric acid |
Examples of Energy Changes could include:
| HEAT GIVEN OUT [EXO]
HEAT TAKEN IN [ENDO] |
e.g. heat released on burning methane gas in a Bunsen burner.
e.g. the drop in temperature when sodium carbonate and ethanoic acid react |
 |
| LIGHT GIVEN OUT | ||
| SOUND GIVEN OUT |
- Physical changes do not involve the production of a new substance.
- Physical changes can involve a change in shape or state (solid, liquid or gas).
