3 Reversible reactions and equilibria Flashcards
What are two reversible reactions?
- Dehydration of copper sulfate crystals.
- Heating ammonium chloride.
What is the dehydration of copper sulfate crystals?
If you heat blue copper (II) sulfate crystals gently, the blue crystals turn to a white powder and water is driven off.
How is the water driven off?
Heating causes the crystals to lose their water of crystallisation and white anhydrous copper (II) sulfate is formed.
What does anhydrous mean?
Without water.
What is the equation for the dehydration of copper sulfate crystals?
CuSO4.5H2O —> CuSO4 + 5H2O
Blue White
What is needed for this reaction to occur?
Heat.
What happens if you add water to the white solid?
It turns blue again; it also becomes very warm.
What is the equation for the rehydration of copper sulfate crystals?
CuSO4 + 5H2O —> CuSO4.5H2O
White Blue
What happens in the during of this reaction?
Heat is released from this reaction.
What has happened with the dehydration and rehydration of the copper sulfate crystals?
The original change has been exactly reversed. Even the heat that you put in has been given out again. This is called a reversible reaction.
What is a reversible reaction?
A reversible reaction is one that can go both ways, in other words, reactants react to form products and products can react to form reactants.
How can we indicate that a reaction is reversible?
With a special arrow.
What does this arrow look like?
⇌
What is heating ammonium chloride?
If you heat ammonium chloride, the white crystals disappear from the bottom of the tube and reappear further up.
What does heating ammonium chloride do?
Heating ammonium chloride splits it into the colourless gases ammonium and hydrogen chloride.
What is the equation when heating ammonium chloride?
NH4CI —> NH3 + HCI
white solid —> colourless gases
What is needed for this reaction to occur?
Heat.
How is this reaction reversed?
Those gases recombine further up the tube, where it is cooler, to form a white solid.
What is the equation used when cooling down ammonium chloride?
NH3 + HCI —> NH4CI
colourless gases —> white solid
What is released from this reaction?
Heat.
When does this reaction reverse?
When the conditions are changed from hot to cool.
What kind of reaction is this an example of?
Thermal decomposition between an acid and a base.
How can this reaction be represented as being reversible?
NH3 + HCI ⇌ NH4CI
