Colour, Temperature Changes and Effervescence
Colour, Temperature Changes and Effervescence
Understanding Chemical Reactions
- A chemical reaction is a process where one or more substances are changed into one or more different substances.
- Chemical reactions involve the rearrangement of atoms in substances.
- They are identified by changes in properties such as colour, temperature and effervescence.
Observation of Colour Changes
- Colour changes are often the most noticeable signs of a chemical reaction taking place.
- An example is the reaction between sodium hydroxide and copper(II) sulphate which produces a blue precipitate.
- Observation of colour change helps to identify certain chemicals.
Understanding Temperature Changes
- Energy is conserved during a chemical reaction hence energy absorbed must equal the energy released.
- If more energy is released than absorbed, the reaction is exothermic and the surroundings warm up. Combustion is an exothermic reaction.
- If more energy is absorbed than released, the reaction is endothermic and the surroundings cool down. Photosynthesis is an endothermic reaction.
Recognising Effervescence
- Effervescence refers to the formation of gas bubbles in a liquid due to a chemical reaction.
- It results from the release of a gas during a chemical reaction.
- For instance, effervescence is observed when an acid reacts with a carbonate or bicarbonate.
- Observing effervescence helps identify certain reactions, especially those involving gases like carbon dioxide, oxygen, or hydrogen.