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
– From the equilibrium partial pressures of products and reactants, calculate the equilibrium
– 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
– 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:
Sample Questions: Chemical Equilibrium
1. a) Write down the equilibrium constant expression for the following reaction:
H2 + I2 Ã¢â€ â€ 2HI
b) At equilibrium the three components of the reaction mixture at 400Ã‚Â°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) Ã¢â€ â€ 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) Ã¢â€ â€ 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) Ã¢â€ â€ 2NO2 (g)
A reaction flask is charged with 3.00 atm of dinitrogen tetroxide gas and 2.00 atm of nitrogen
dioxide gas. At 25Ã‚Â°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.
5. Two species of Phosphorous Chloride, PCl3 and PCl5, coexist in equilibrium through:
Ã°Ââ€˜Æ’Ã°ÂÂÂ¶Ã°Ââ€˜â„¢3 (Ã°Ââ€˜â€) + Ã°ÂÂÂ¶Ã°Ââ€˜â„¢2 (Ã°Ââ€˜â€) Ã¢â€ â€ Ã°Ââ€˜Æ’Ã°ÂÂÂ¶Ã°Ââ€˜â„¢5 (Ã°Ââ€˜â€)
At 250oC, an equilibrium mixture in a 2.50L flask contains 0.105g Ã°Ââ€˜Æ’Ã°ÂÂÂ¶Ã°Ââ€˜â„¢5, 0.220g Ã°Ââ€˜Æ’Ã°ÂÂÂ¶Ã°Ââ€˜â„¢3 , and
2.12g Ã°ÂÂÂ¶Ã°Ââ€˜â„¢2. What are the values of Kc and Kp for this reaction?
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