If a reaction has an equilibrium constant just greater than 1, what type of reaction is it?

The fact that the equilibrium constant is just greater than 1 means that the reaction is reversible and the products are favored.

Explanation:

In general an equilibrium reaction may be represented by:

Reactant₁ + Reactant₂ ⇄ Product₁ + Product₂

The double arrow means that the reactants on the left side yield the products on the right side, but also the products of the right side yield the reactants on the left side.

Of course, the number of reactants and products is not limited (may be one or more reactants and one or more products).

You might write two separete equations to visualize that:

Reactants → Products: this is called the forward reaction; Reactants ← Products: this is called the reverse reaction.

Then, you see the reversible part of the equation.

The expression of the equilibrium constant, Keq, in a very simplified form could be:

Keq = [Product₁]ᵃ [Product₂]ᵇ / [Reactant₁]ⁿ [Reactant₂]ˣ

Where the superscripts are the respective stoichiometric coefficients on the balanced chemical equation, and the brackets indicate molar concentrations (molarity).

So, when Keq > 1, means that the numerator (the products) is greater than the denominator (the reactants), so the products are favored.

When Keq is a big number, much greater than 1, means that, for certain effects, the chemical equation might be considered irreversible, this reaction goes almost to completion.