Hydrogen sulfide (H2S) is a common and troublesome pollutant in industrial wastewaters. One way to remove H2S is to treat the water with chlorine, in which case the following reaction occurs: H2S(aq) + Cl2(aq) → S(s) + 2 H+(aq) + 2 Cl-(aq). The rate of this reaction is first order in each reactant. The rate constant for the disappearance of H2S at 28°C is 3.5 * 10^-2 M^-1 s^-1. If at a given time the concentration of H2S is 2.0 * 10^-4 M and that of Cl2 is 0.025 M, what is the rate of formation of Cl-?

Verified step by step guidance

1. Step 1: Understand the rate law for the reaction. Since the reaction is first order in each reactant, the rate law can be expressed as: rate = k[H2S][Cl2], where k is the rate constant.
2. Step 2: Identify the given values. The rate constant k is 3.5 * 10^-2 M^-1 s^-1, the concentration of H2S is 2.0 * 10^-4 M, and the concentration of Cl2 is 0.025 M.
3. Step 3: Substitute the given values into the rate law equation to find the rate of the reaction: rate = (3.5 * 10^-2 M^-1 s^-1)(2.0 * 10^-4 M)(0.025 M).
4. Step 4: Recognize that the rate of formation of Cl- is related to the rate of the reaction. According to the balanced chemical equation, 2 moles of Cl- are produced for every mole of H2S that reacts.
5. Step 5: Calculate the rate of formation of Cl- by multiplying the rate of the reaction by 2, since 2 moles of Cl- are formed per mole of H2S consumed.

Key Concepts

Reaction Rate

The reaction rate is a measure of how quickly reactants are converted into products in a chemical reaction. It is often expressed in terms of the change in concentration of a reactant or product over time. In this case, the rate of the reaction is first order with respect to both H2S and Cl2, meaning that the rate depends linearly on the concentration of each reactant.

Rate Law

The rate law is an equation that relates the rate of a chemical reaction to the concentration of its reactants, each raised to a power corresponding to its order in the reaction. For the given reaction, the rate law can be expressed as rate = k[H2S][Cl2], where k is the rate constant. This relationship allows us to calculate the rate of formation of products based on the concentrations of the reactants.

Stoichiometry

Stoichiometry involves the quantitative relationships between the amounts of reactants and products in a chemical reaction. In the provided reaction, the stoichiometry indicates that for every mole of H2S that reacts, two moles of Cl- are produced. This relationship is crucial for determining the rate of formation of Cl- based on the rate of the reaction and the concentrations of the reactants.