C8.6 - Reversible reactions Flashcards
What happens in most chemical reactions?
In most chemical reactions, the reactants react completely to form the products
In most chemical reactions, the reactants react completely to form the products.
How do you show this?
You show this by using an arrow pointing from the reactants to the products
In most chemical reactions, the reactants react completely to form the products.
However, what happens in some reactions?
In some reactions, the products can react together to make the original reactants again
Reversible reaction
A reversible reaction is a reaction in which the products can re-form the reactants
Why are 2 ‘half-arrows’ used in the equation of a reversible reaction?
2 ‘half-arrows’ are used in the equation of a reversible reaction, because a reversible reaction can go in both directions
It is very difficult to get a what?
It is very difficult to get a solution that is exactly neutral
It is very difficult to get a solution that is exactly neutral.
What can you use to tell when just the right amount of acid has been added, when neutralising an alkaline solution?
When neutralisation an alkaline solution with acid, you can use an indicator to tell when just the right amount of acid had been added
What does an indicator do?
An indicator forms compounds that are different colours in:
- Acidic solutions
- Alkaline solutions
Litmus
Litmus is a complex molecule
Litmus is a complex molecule.
How can litmus be represented?
Litmus can be represented as HLit, where H is hydrogen
What colour is HLit?
HLit is red
HLit is red.
What happens if you add alkali?
If you add alkali, HLit turns into the Lit- ion by losing a H+ ion
If you add alkali, HLit turns into the Lit- ion by losing a H+ ion.
What colour is Lit-?
Lit- is blue
HLit is red.
If you add alkali, HLit turns into the Lit- ion by losing a H+ ion.
What happens if you then add more acid?
If you then add more acid, blue Lit- changes back to red HLit
The neutralisation of acids is a reversible reaction.
What do other reversible reactions involve?
Other reversible reactions involve salts
The neutralisation of acids is a reversible reaction.
Other reversible reactions involve salts.
Example
For example: Hydrated copper(II) sulfate (blue) Anhydrous copper(II) sulfate (white) + Water
What do indicators undergo?
Indicators undergo reversible reactions
When does blue litmus paper turn red?
Blue litmus paper turns red in acidic solutions
When does red litmus paper turn blue?
Red litmus paper turns blue in alkaline solutions
What happens when you heat ammonium chloride?
When you heat ammonium chloride, a reversible reaction takes place
An example of a thermal decomposition reaction
An example of a thermal decomposition reaction is when ammonium chloride forms:
1. Ammonia gas
2. Hydrogen chloride gas
after you heat it
The word equation for the thermal decomposition of ammonium chloride
The word equation for the thermal decomposition of ammonium chloride is:
heat
Ammonium chloride —> Ammonia + Hydrogen chloride
When you heat ammonium chloride, a reversible reaction takes place.
Ammonium chloride breaks down on heating to form ammonia gas and hydrogen chloride gas.
What do the 2 hot gases do?
The 2 hot gases rise up the test tube
When you heat ammonium chloride, a reversible reaction takes place.
Ammonium chloride breaks down on heating to form ammonia gas and hydrogen chloride gas.
The 2 hot gases rise up the test tube.
What happens when they cool down near the mouth of the tube?
When the 2 hot gases cool down near the mouth of the tube, they react with each other
In most chemical reactions, the reactants react completely to form the products.
In some reactions, the products can react together to make the original reactants again.
This is called a what reaction?
This is called a reversible reaction
If you add alkali, HLit turns into the Lit- ion by losing a H+ ion.
Lit- is blue, so HLit turns from what to what if you add alkali?
Lit- is blue, so HLit turns from red to blue if you add alkali
Indicators undergo reversible reactions, doing what to show you whether solutions are what?
Indicators undergo reversible reactions, changing colour to show you whether solutions are:
1. Acidic
Or,
2. Alkaline
When you heat ammonium chloride, a reversible reaction takes place.
Ammonium chloride breaks down on heating to form what?
Ammonium chloride breaks down on heating to form:
- Ammonia gas
- Hydrogen chloride gas
When you heat ammonium chloride, a reversible reaction takes place.
Ammonium chloride breaks down on heating to form ammonia gas and hydrogen chloride gas.
The 2 hot gases rise up the test tube.
When the 2 hot gases cool down near the mouth of the tube, they react with each other.
The gases do what again?
The gases re-form ammonium chloride again
When you heat ammonium chloride, a reversible reaction takes place.
Ammonium chloride breaks down on heating to form ammonia gas and hydrogen chloride gas.
The 2 hot gases rise up the test tube.
When the 2 hot gases cool down near the mouth of the tube, they react with each other.
The gases re-form ammonium chloride again.
What forms on the inside of the glass?
The white ammonium chloride solid forms on the inside of the glass
