MYP Chemistry Reversible Reactions Notes

What Is a Reversible Reaction, and How Is It Different from an Irreversible Reaction?

In chemistry, reactions can be:

1. Irreversible (one way), or
2. Reversible (two-way).

Irreversible Reactions

An irreversible reaction is a reaction that effectively goes in one direction only:

Reactants → Products

1. Once the reactants have formed products, they do not easily change back into the original substances.
2. These reactions often release a lot of energy and produce very stable products.

Reversible Reactions

A reversible reaction can go in both directions:

Reactants ⇌ Products

1. The products can react again to re-form the original reactants.
2. Both the forward and reverse reactions can occur in the same system, often at the same time.

Key Differences

1. Irreversible reactions
   1. Proceed in one direction only.
   2. Products are usually very stable and do not easily revert to reactants.
   3. Often release a large amount of energy and go to completion.
2. Reversible reactions
   1. Can proceed in both forward and reverse directions.
   2. Products can react to reform reactants.
   3. Can reach a state of dynamic equilibrium in a closed system, where
      1. the rate of the forward reaction = the rate of the reverse reaction,
      2. and the concentrations of reactants and products remain constant (but not necessarily equal).

How Do We Represent Reversible Reactions with Symbols and Dynamic Models?

Symbolic Representation

A general reversible reaction is written as: $$\mathrm{A}+\mathrm{B} \rightleftharpoons \mathrm{C}+\mathrm{D}$$

1. Forward reaction: $$\mathrm{A}+\mathrm{B} \to \mathrm{C}+\mathrm{D}$$
2. Reverse reaction: $$\mathrm{C}+\mathrm{D} \to \mathrm{A}+\mathrm{DB}$$