C2.5 - Exothermic and Endothermic Reactions Flashcards
What always happens whenever chemical reactions occur?
Whenever chemical reactions occur, energy is transferred to or from the surroundings.
What is an exothermic reaction?
An exothermic reaction is one that transfers energy to the surroundings - usually in the form of heat and usually indicated by a rise in temperature.
What are some examples of exothermic reactions?
Combustion
Oxidation
Neutralisation
What are some uses of exothermic reactions?
Self heating cans - chemicals combine to heat coffee
Handwarmers - oxidation of iron in the air with a salt solution catalyst
What is an endothermic reaction?
An endothermic reaction is one that takes in energy from the surroundings - usually in the form of heat and is usually shown by a fall in temperature.
Are endothermic reactions more or less frequent than exothermic reactions?
They are less common
What are some examples and uses of endothermic reactions?
Thermal decomposition
Sports injury packs - take in heat and the pack becomes cold
What happens in a typical reaction?
A + B -> C
What is a reversible reaction (in terms of energy release)?
In a reversible reaction, if the reaction is endothermic in one direction, it will be exothermic in the other direction.
What is an example of a reversible reaction?
The thermal decomposition of hydrated copper sulfate.
Define hydrated
Contains water
What is the word equation for hydrated copper sulfate?
Hydrated copper sulfate -> anhydrous copper sulfate + water
Explain the thermal decomposition of hydrated copper sulfate.
If you heat the hydrated copper sulfate crystals it drives the water off and leaves white anhydrous copper sulfate powder. This is endothermic.
If a couple of water droplets are added to the powder then blue crystals return. This is exothermic.
