What is meant when chemists say that the equilibrium position of a reaction "lies to the left"?
Chemical reactions are generally of two types. In many chemical reactions the reactants combine to form products - the reactants are gone and the products are all that is left. Examples are when a solid precipitate forms as one of the products or a gas is released as one of the products.
Another general type is when the reactants and products are both present. What is happening is that the reactants are combining to form one or more products but the products are also breaking down to reform the reactants. In a reaction of this type, you measure the relative amount of reactants and products to determine whether there are more products or more reactants present in the equilibrium mixture. If there are more reactants than products the equilibrium "lies to the left" and if there are more products than reactants then the equilibrium "lies to the right". The reaction of H2 with N2 to form NH3 would be an example of an equilibrium reaction.
The equilibrium position of a reaction lies to the left means the rate of the backward reaction is greater than the rate of the forward reaction. Which means the products are converting back in to the reactants.
At equilibrium the rate of forward reaction will be equal to the rate of backward reaction.