Question

(a) What is meant by the term reaction rate? (b) Name three factors that can affect the rate of a chemical reaction. (c) What information is necessary to relate the rate of disappearance of reactants to the rate of appearance of products?

Short answer

(a) Reaction rate refers to the speed at which a chemical reaction occurs, often expressed as the change in concentration of a reactant or product per unit time: \(Reaction \, rate = \frac{Change \, in \, concentration \, of \, reactant \, or \, product}{Time \, taken}\). (b) Three factors affecting reaction rates are: concentration of reactants, temperature, and presence of a catalyst. (c) To relate the rate of disappearance of reactants to the rate of appearance of products, we need to know the stoichiometry of the balanced chemical equation, as the stoichiometric coefficients indicate the ratio at which reactants are consumed and products are formed.

Step-by-step solution

Part (a): Definition of Reaction Rate

Reaction rate refers to the speed at which a chemical reaction occurs. It is often expressed as the change in concentration of a reactant or a product per unit time. Mathematically, it can be represented as: \(Reaction \, rate = \frac{Change \, in \, concentration \, of \, reactant \, or \, product}{Time \, taken}\)

Part (b): Factors Affecting Reaction Rates

There are several factors that can affect the rate of a chemical reaction. Here are three common factors: 1. Concentration of reactants: Increasing the concentration of reactants typically increases the reaction rate, as there are more particles available to collide and react with each other. 2. Temperature: As the temperature increases, the average kinetic energy of the particles increases, resulting in more frequent and energetic collisions between reactant particles. This generally leads to an increase in the reaction rate. 3. Presence of a catalyst: A catalyst is a substance that speeds up a reaction without being consumed in the process. It does this by providing an alternative reaction pathway with lower activation energy, making it easier for the reactants to transform into products and increasing the reaction rate.

Part (c): Relating Disappearance of Reactants to Appearance of Products

To relate the rate of disappearance of reactants to the rate of appearance of products, we need to know the stoichiometry of the balanced chemical equation for the reaction. The stoichiometric coefficients in the balanced equation indicate the ratio at which reactants are consumed and products are formed. For example, consider a general reaction: \(aA + bB \rightarrow cC + dD\) where A and B are reactants, C and D are products, and a, b, c, and d are their respective stoichiometric coefficients. The rate of disappearance of the reactants A and B can be expressed as: \(-\frac{1}{a}\frac{d[A]}{dt}\) and \(-\frac{1}{b}\frac{d[B]}{dt}\) Similarly, the rate of appearance of the products C and D can be expressed as: \(\frac{1}{c}\frac{d[C]}{dt}\) and \(\frac{1}{d}\frac{d[D]}{dt}\) Using these expressions and the stoichiometric coefficients, we can relate the rate of disappearance of reactants to the rate of appearance of products in a chemical reaction.