Which statement describes a chemical reaction at equilibrium?
Reactant molecules and product molecules have the same velocity.
Molecules of reactants and products collide with the same frequency.
The concentrations of reactants and products are equimolar.
Reactants and products are consumed and formed at the same rate.
The statement that describes a chemical reaction at equilibrium is: "Reactants and products are consumed and formed at the same rate."
To understand why this statement describes a chemical reaction at equilibrium, let's first define what equilibrium means in the context of a chemical reaction. Equilibrium is a state in a chemical reaction where the forward reaction rate is equal to the backward reaction rate, resulting in no net change in the concentrations of the reactants and products over time.
Now, let's break down each option:
1. Reactant molecules and product molecules have the same velocity: This statement doesn't describe equilibrium. The velocity of individual molecules is not directly related to the equilibrium state of a reaction. In a chemical reaction, the equilibrium state is determined by the rates of the forward and backward reactions, not the velocity of individual molecules.
2. Molecules of reactants and products collide with the same frequency: This statement also does not accurately describe equilibrium. While the collision frequency may play a role in determining the reaction rate, it doesn't necessarily indicate that the reaction is at equilibrium. Equilibrium is achieved when the rates of the forward and backward reactions are equal, not just the collision frequency.
3. The concentrations of reactants and products are equimolar: This statement accurately describes equilibrium. In an equilibrium state, the concentrations of reactants and products reach a constant value, which can be equimolar or in different ratios depending on the balanced chemical equation. However, it's important to note that equimolar concentrations are not a requirement for a reaction to be at equilibrium.
4. Reactants and products are consumed and formed at the same rate: This statement accurately describes equilibrium. In a system at equilibrium, the forward and backward reactions occur at the same rate. As a result, the concentrations of reactants and products remain constant over time since they are being consumed and formed at the same rate.
Therefore, the correct answer is: "Reactants and products are consumed and formed at the same rate."