Ch.15 - Chemical Equilibrium
Chapter 15, Problem 1
The equilibrium concentrations in a gas mixture at a particular temperature are 0.13 M H2, 0.70 M I2, and 2.1 M HI. What equilibrium concentrations are obtained at the same temperature when 0.20 mol of HI is injected into an empty 500.0-mL container?

1
Step 1: Calculate the initial concentration of HI after injection. Use the formula \( C = \frac{n}{V} \), where \( n \) is the number of moles and \( V \) is the volume in liters. Convert 500.0 mL to liters.
Step 2: Write the balanced chemical equation for the reaction: \( \text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g) \).
Step 3: Determine the reaction quotient \( Q_c \) using the initial concentrations: \( Q_c = \frac{[\text{HI}]^2}{[\text{H}_2][\text{I}_2]} \). Compare \( Q_c \) with the equilibrium constant \( K_c \) to predict the direction of the shift.
Step 4: Set up an ICE (Initial, Change, Equilibrium) table to track the changes in concentrations as the system reaches equilibrium. Use \( x \) to represent the change in concentration for \( \text{H}_2 \) and \( \text{I}_2 \).
Step 5: Solve for \( x \) using the equilibrium expression \( K_c = \frac{[\text{HI}]^2}{[\text{H}_2][\text{I}_2]} \) and the values from the ICE table. Calculate the new equilibrium concentrations.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chemical Equilibrium
Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In a closed system, this state can be described by the equilibrium constant (K), which relates the concentrations of the products and reactants at equilibrium. Understanding this concept is crucial for predicting how changes in concentration affect the system.
Recommended video:
Guided course
Chemical Equilibrium Concepts
Le Chatelier's Principle
Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust to counteract the change and restore a new equilibrium. This principle helps predict how the addition of a substance, such as HI in this case, will shift the equilibrium position, affecting the concentrations of all species involved.
Recommended video:
Guided course
Le Chatelier's Principle
Concentration Calculations
Concentration calculations involve determining the molarity (M) of a solution, which is defined as the number of moles of solute per liter of solution. In this scenario, after injecting HI into a 500.0-mL container, it is essential to calculate the new concentrations of H2, I2, and HI to analyze the system's response to the added reactant and establish the new equilibrium state.
Recommended video:
Guided course
Calculate Concentration of the Basic Form
Related Practice