Trinity College Dublin Chemical Equilibrium Questions

  

Description

Please answer all 5 questions in the document attached. The questions are on page 2 and 3.

Chapter Learning Outcomes
– Given any balanced chemical equation representing a homogeneous or heterogeneous
equilibrium, write the equilibrium equation
– From the equilibrium concentrations of products and reactants, calculate the equilibrium
constant Kc
– From the equilibrium partial pressures of products and reactants, calculate the equilibrium
constant Kp
– From a value of Kc and a balanced equation, calculate Kp, and vice versa
– From the value of Kc or Kp, determine whether mainly products or mainly reactants exist at
equilibrium
– For a given mixture of reactants and products, determine whether a system is at equilibrium.
If it is not, determine the direction in which the reaction must go to achieve equilibrium
– Given Kc and initial concentrations of reactants and/or products, calculate the final
concentration of reactants and/or products
– Determine the reaction direction when a system at equilibrium reacts to a stress applied to
the system, including changes in concentrations, pressure and volume, or temperature
Notes regarding the exam:
1
Sample Questions: Chemical Equilibrium
1. a) Write down the equilibrium constant expression for the following reaction:
H2 + I2 ↔ 2HI
b) At equilibrium the three components of the reaction mixture at 400°C are present at the
following concentrations: [H2 ] = 1.065 mol L-1, [I2 ] = 0.065 mol L-1 and [HI] = 1.87 mol L-1.
What is the equilibrium constant for this equilibrium reaction?
c) At some point during the reaction, we measure the concentrations and we obtain the
following values: [H2 ] = 1.3 mol L-1, [I2 ] = 0.7 mol L-1 and [HI] = 0.3 mol L-1. In which
direction must the reaction proceed for equilibrium to be reached?
2. Consider the following reaction:
2NO(g) + Cl2 (g) ↔ 2NOCl(g)
At equilibrium the three gases are present at the following partial pressures: NO = 24.0 kPa,
Cl2 = 60.8 kPa and NOCl = 135 kPa. Calculate the Kp for this reaction.
3. Consider the following reaction:
C2 H4 (g) + H2 (g) ↔ C2 H6 (g)
What is the concentration for each substance at equilibrium if the initial concentration of
C2 H4 = 0.335 M and that of hydrogen is 0.526 M?
Data: The equilibrium constant of the reaction is 0.99.
4. Consider the following reaction:
N2 O4 (g) ↔ 2NO2 (g)
A reaction flask is charged with 3.00 atm of dinitrogen tetroxide gas and 2.00 atm of nitrogen
dioxide gas. At 25°C, the gases are allowed to reach equilibrium. The pressure of the nitrogen
dioxide was found to have decreased by 0.952 atm. Estimate the value of Kp for this system.
2
5. Two species of Phosphorous Chloride, PCl3 and PCl5, coexist in equilibrium through:
𝑃𝐶𝑙3 (𝑔) + 𝐶𝑙2 (𝑔) ↔ 𝑃𝐶𝑙5 (𝑔)
At 250oC, an equilibrium mixture in a 2.50L flask contains 0.105g 𝑃𝐶𝑙5, 0.220g 𝑃𝐶𝑙3 , and
2.12g 𝐶𝑙2. What are the values of Kc and Kp for this reaction?
3

Purchase answer to see full
attachment