Problem 17 - Chemistry The Central Science

Question

(a) What is meant by the term reaction rate? (b) Name three factors that can affect the rate of a chemical reaction. (c) Is the rate of disappearance of reactants always the same as the rate of appearance of products?

Step-by-Step Solution

Answer

(a) Reaction rate refers to the change in the concentration of reactants or products per unit time, typically represented as moles per liter per second (M/s). (b) Three factors that can affect the rate of a chemical reaction include the concentration of reactants, temperature, and the presence of catalysts. (c) The rate of disappearance of reactants is directly related to the rate of appearance of products, but their rates may not always be the same. This depends on their stoichiometric coefficients in the balanced chemical reaction equation.

Step 1: (a) Defining "reaction rate"

Reaction rate refers to the speed at which a chemical reaction occurs, or more specifically, the change in the concentration of reactants or products per unit time. It is typically represented as moles per liter per second (M/s).

Step 2: (b) Factors affecting reaction rate

There are several factors that can influence the rate of a chemical reaction: 1. Concentration of reactants: As the concentration of the reactants increases, the rate of reaction generally speeds up because there is an increased likelihood that the reacting particles will collide and interact with each other. 2. Temperature: An increase in temperature generally results in an increased reaction rate, as the particles have more kinetic energy and collide more frequently and with greater force. This increases the chances of successful collisions, which leads to faster reactions. 3. Catalysts: Catalysts are substances that can significantly speed up the rate of a chemical reaction without being consumed by the reaction itself. They work by lowering the activation energy needed for the reaction to occur (i.e., they provide an alternative reaction pathway with a lower energy barrier).

Step 3: (c) Relationship between reactant disappearance and product appearance rates

In most chemical reactions, the rate of disappearance of reactants is directly related to the rate of appearance of products. According to the law of conservation of mass, matter cannot be created or destroyed, only converted from one form to another. Thus, when reactants are transformed into products, the total amount of mass in the reaction system should remain the same. However, if there are multiple reactants and products involved in a chemical reaction, we can't say that the rate of disappearance of one reactant is the same as the rate of appearance of one product. This is determined by their stoichiometric coefficients in the balanced chemical reaction equation. If the stoichiometric coefficients are the same for reactants and products, their rates of disappearance and appearance will be equivalent. Otherwise, we must compare the rates of disappearance and appearance according to their stoichiometric coefficients.