A negative rate of reaction signifies that the concentration of reactants is decreasing over time.

To elaborate, the rate of a chemical reaction quantifies the speed at which the concentration of reactants diminishes or the concentration of products increases. This rate is typically expressed as a change in concentration per unit of time. When the rate of reaction is negative, it indicates that reactants are being consumed to produce products, resulting in a decline in their concentration over time.

The sign of the rate of reaction is influenced by the direction in which the reaction is occurring. If the reaction is progressing in the forward direction—transforming reactants into products—the rate of reaction is positive. This occurs because the concentration of reactants decreases (as they are consumed) while the concentration of products increases. Conversely, if the reaction is moving in the reverse direction—converting products back into reactants—the rate of reaction is negative. In this case, the concentration of products diminishes (as they are consumed), leading to an increase in the concentration of reactants.

In certain scenarios, a reaction may proceed in both the forward and reverse directions simultaneously, which is termed a reversible reaction. In reversible reactions, the rates of the forward and reverse processes can differ. If the forward reaction rate exceeds that of the reverse reaction, the overall rate of reaction is positive. However, if the reverse reaction rate is greater than the forward reaction rate, the overall rate of reaction becomes negative.

In summary, a negative rate of reaction indicates that the reaction is occurring in the reverse direction, leading to an increase in the concentration of reactants and a decrease in the concentration of products. This concept is crucial for understanding the dynamics of chemical reactions and is fundamental to the study of chemistry.