Question 1

The standard Gibbs energy of reaction for the equilibrium 2 NO₂(g) ∏ N₂O₄(g) Is -4.73 kJ mol^-1 at 298 K. Calculate the value of the equilibrium constant at this temperature.

Accepted Answer

The equilibrium constant (K) is related to the standard Gibbs energy of reaction (ΔG°) by the equation:ΔG° = -RTlnKwhere R is the gas constant (8.314 J mol^-1 K^-1) and T is the temperature in Kelvin.Substituting the given values into the equation, we get:-4.73 kJ mol^-1 = -(8.314 J mol^-1 K^-1)(298 K)lnKSolving for K, we get:K = e^(-4.73 kJ mol^-1 / (8.314 J mol^-1 K^-1)(298 K)) = 6.75Therefore, the value of the equilibrium constant at 298 K is 6.75.

Question 2

Calculate the standard reaction Gibbs energy for the reaction 2 N₂O₅(g) 4 NO₂(g) + O₂(g) at a temperature of 298 K. The standard Gibbs energies of formation of the components at this temperature are given in the table below. $\begin{array}{lc} & \Delta \mathrm{f} G^{e}(298 \mathrm{~K}) / \mathrm{kJ} \mathrm{mol}^{-1} \ \mathrm{N}_{2} \mathrm{O}_{5} \ & +118.0 \ \mathrm{NO}_{2} \ & +51.8\ \mathrm{O}_{2}\ &0\ \end{array}$

Accepted Answer

C

Question 3

The equilibrium constant for the reaction H₂(g) + Br₂(g) ∏ 2 HBr(g) Is 2.1 *10⁹ at 298 K. What is the value of the equilibrium constant for the reaction ½ H₂(g) + ½ Br₂(g) ∏ HBr(g) at this temperature?

Accepted Answer

D

Question 4

The value of the equilibrium constant for the electrochemical reaction MnO₄^-(aq) + 2 H⁺(aq) + ½ Cl₂(g) ∏ Mn²⁺(aq) + ClO₃^-(aq) + H₂O(aq) Is 5.88 *10^-5. What is the value of the equilibrium constant for the reverse reaction?

Accepted Answer

The equilibrium constant for the reverse reaction is the reciprocal of the equilibrium constant for the forward reaction. Therefore, if the forward reaction has an equilibrium constant of $5.88 \times 10^{-5}$, the reverse reaction's equilibrium constant would be $1 / (5.88 \times 10^{-5})$, which is approximately $1.70 \times 10^{5}$, or as presented in scientific notation, $17.0 \times 10^{4}$.

Question 5

The standard Gibbs energy of reaction for the thermal decomposition of ammonium chloride, NH₄Cl NH₄Cl(s) ∏ NH₃(g) + HCl(g) Is +35.0 kJ mol^-1 at 225 °C. Calculate the partial pressure of ammonia, NH₃, gas produced when ammonium chloride is allowed to decompose at a pressure of 1 bar at this temperature.

Accepted Answer

The correct answer is A because the partial pressure of ammonia, NH3, gas produced when ammonium chloride is allowed to decompose at a pressure of 1 bar at this temperature is 1460 Pa.

Question 6

When phosphorus pentachloride, PCl₅, is heated at a constant pressure of exactly 1 bar to a temperature of 1400 K, the amount of phosphorus pentachloride decreases by 20.7% because of dissociation to phosphorus trichloride, PCl₃, and chlorine, Cl₂. Determine the equilibrium constant at this temperature.

Accepted Answer

The equilibrium constant (K) can be calculated using the degree of dissociation and the initial concentration of PCl5. Given that 20.7% of PCl5 dissociates, we can set up an equilibrium expression involving the concentrations of PCl5, PCl3, and Cl2 at equilibrium. The calculation involves using the stoichiometry of the reaction and the given percentage of dissociation to find the equilibrium concentrations of the reactants and products, and then applying these to the formula for the equilibrium constant. The correct answer involves detailed calculations that account for the change in concentration due to the dissociation and the stoichiometry of the reaction.

Question 7

When lead (II) oxide, PbO, is allowed to react with oxygen, O₂, at a temperature of 823 K and standard pressure through the reaction PbO(s) + ½O₂(g) ∏ PbO₂(s) The partial pressure of oxygen at equilibrium is 11.6 Pa. Determine the standard Gibbs energy of reaction at this temperature.

Accepted Answer

The standard Gibbs energy of reaction can be calculated using the equation ΔG° = -RTlnKp, where R is the gas constant (8.314 J mol^-1 K^-1), T is the temperature in Kelvin, and Kp is the equilibrium constant related to the partial pressures of the gases involved. Given the partial pressure of oxygen at equilibrium is 11.6 Pa, and since the reaction involves ½ mole of O2, Kp = (P_O2)^1/2 = (11.6 Pa)^1/2. Plugging the values into the equation and converting units appropriately gives a ΔG° close to -31.0 kJ mol^-1, making choice A correct.

Question 8

The value of the equilibrium constant for the gas-phase reaction 2 NOCl(g) ∏ 2 NO(g) + Cl₂(g) Is K = 7.65 * 10^-8 at 298.15 K. Determine the value of the equilibrium constant expressed in terms of concentrations, K_c, at this temperature.

Accepted Answer

The equilibrium constant expressed in terms of concentrations, K_c, is related to the equilibrium constant expressed in terms of partial pressures, K_p, by the following equation:K_c = K_p(RT)^Δnwhere R is the ideal gas constant, T is the temperature in Kelvin, and Δn is the change in the number of moles of gas in the reaction.In this case, Δn = 2 - 3 = -1, so:K_c = K_p(RT)^-1Substituting the given values into this equation, we get:K_c = (7.65 × 10^-8)(0.0821)(298.15)^-1 = 3.10 × 10^-9

Question 9

For sulfur hexafluoride, SF₆, the standard Gibbs energy of formation of is -992 kJ mol^-1 and the standard entropy of formation is -350 J K^-1 mol^-1 at 298 K. Assuming that the values of the enthalpy and entropy of formation vary little with temperature, estimate the standard Gibbs energy of formation of sulfur hexafluoride at 348 K.

Accepted Answer

The answer of For sulfur hexafluoride, SF₆, the standard Gibbs...

Question 10

The value of the equilibrium constant for the reaction C₂H₄(g) + H₂O(g) ∏ C₂H₅OH(g) Is 9.920 at 423 K and 6.397 at 523 K. Determine the average value of the standard enthalpy of reaction over this temperature range.

Accepted Answer

The correct answer is A.The average value of the standard enthalpy of reaction can be calculated using the van't Hoff equation:ln(K2/K1) = -ΔH°/R (1/T2 - 1/T1)where K1 and K2 are the equilibrium constants at temperatures T1 and T2, respectively, ΔH° is the standard enthalpy of reaction, and R is the gas constant.Substituting the given values into the equation, we get:ln(9.920/6.397) = -ΔH°/R (1/523 - 1/423)Solving for ΔH°, we get:ΔH° = -8.1 kJ mol-1

Question 11

Calculate the concentration of hydronium, H₃O⁺, ions in a solution of pH = 11.2.

Accepted Answer

The answer of Calculate the concentration of hydronium, H₃O⁺, ions...

Question 12

The pK_a of 2-chloropropanoic acid, CH₃CHClCO₂H, is 2.83. Calculate the Gibbs energy for the dissociation CH₃CHClCO₂H(aq) + H₂O(aq) ⇌ CH₃CHClCO₂^-(aq) + H₃O⁺(aq) At a temperature of 298 K.

Accepted Answer

The Gibbs energy for the dissociation can be calculated using the equation:ΔG = -RTlnKwhere R is the gas constant (8.314 J/mol·K), T is the temperature in Kelvin (298 K), and K is the equilibrium constant.The equilibrium constant for the dissociation of 2-chloropropanoic acid can be calculated using the pK_a:pK_a = -logKK = 10^-pK_aK = 10^-2.83 = 1.48 × 10^-3Substituting the values of R, T, and K into the equation for ΔG, we get:ΔG = -8.314 J/mol·K × 298 K × ln(1.48 × 10^-3)ΔG = +16.1 kJ/molTherefore, the correct answer is A: +16.1 kJ mol^-1.

Question 13

The concentration of OH^- ions in a solution is 5.62 mmol dm^-3. Determine the pH of the solution.

Accepted Answer

The concentration of OH- ions is given as 5.62 mmol dm^-3, which is equivalent to 5.62 x 10^-3 mol dm^-3. The pOH of the solution can be calculated using the formula pOH = -log[OH-], which gives pOH = -log(5.62 x 10^-3) ≈ 2.25. Since pH + pOH = 14 for aqueous solutions at 25°C, the pH of the solution is 14 - 2.25 = 11.75, which rounds to 11.7.

Question 14

The pK_b of the base cyclohexamine, C₆H₁₁NH₂, is 3.36. What is the pK_a of the conjugate acid, C₆H₁₁NH₃⁺?

Accepted Answer

The pKa of the conjugate acid of a base is related to the pKb of the base by the equation pKa + pKb = 14. Given that the pKb of cyclohexamine is 3.36, the pKa of its conjugate acid can be calculated as 14 - 3.36 = 10.64.

Question 15

Determine the pH of an aqueous solution of benzoic acid, C₆H₅COOH, of concentration 0.064 mol dm^-3. The pK_a of benzoic acid is 4.19.

Accepted Answer

The pH of a weak acid solution can be calculated using the formula: pH = 0.5 * (pKa - log C), where C is the concentration of the acid. Substituting the given values: pH = 0.5 * (4.19 - log 0.064) ≈ 2.69.

Question 16

Calculate the pH of an aqueous solution of sodium hydrogenphosphite, NaHPO₃. For phosphorous acid, H₂PO₃, pK_a1 = 2.00 and pK_a2 = 6.59.

Accepted Answer

The pH of the solution can be approximated by the average of the pKa1 and pKa2 of phosphorous acid, since sodium hydrogenphosphite (NaH2PO3) is a salt of the diprotic phosphorous acid (H3PO3) and will partially dissociate in water to form H2PO3^- ions, which can then lose a proton to form HPO3^2- ions. The average of the pKa values (2.00 and 6.59) gives a pH of approximately 4.30.

Question 17

Calculate the pH of a solution produced by mixing 4.3 cm³ of 0.100 mol dm^-3 potassium hydroxide, KOH, solution to 50.0 cm³ of 0.136 mol dm^-3 propanoic acid, C₂H₅COOH, solution. The pK_a of propanoic acid is 4.87.

Accepted Answer

To find the pH of the solution, first, we need to calculate the moles of KOH and propanoic acid. For KOH: $4.3 \, \text{cm}^3 \times 0.100 \, \text{mol dm}^{-3} = 0.00043 \, \text{mol}$. For propanoic acid: $50.0 \, \text{cm}^3 \times 0.136 \, \text{mol dm}^{-3} = 0.0068 \, \text{mol}$. When KOH is mixed with propanoic acid, it neutralizes some of the acid, forming water and the propanoate ion. The reaction consumes all of the KOH, leaving $0.0068 - 0.00043 = 0.00637 \, \text{mol}$ of propanoic acid unreacted. The concentration of the propanoic acid in the final solution (which has a volume of $4.3 + 50.0 = 54.3 \, \text{cm}^3$ or $0.0543 \, \text{dm}^3$) is $0.00637 \, \text{mol} / 0.0543 \, \text{dm}^3 = 0.117 \, \text{mol dm}^{-3}$. Using the Henderson-Hasselbalch equation, $ \text{pH} = \text{p}K_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) $, where $[\text{A}^-]$ is the concentration of the propanoate ion (which is equal to the initial moles of KOH, $0.00043 \, \text{mol}$, divided by the total volume in dm$^3$, $0.0543$, giving $0.00792 \, \text{mol dm}^{-3}$) and $[\text{HA}]$ is the concentration of the unreacted propanoic acid. Plugging in the numbers: $ \text{pH} = 4.87 + \log \left( \frac{0.00792}{0.117} \right) $, which approximates to a pH of 3.67.

Question 18

When an excess of copper (II) iodate, Cu(IO₃)₂, is added to water at 298 K, the equilibrium concentration of copper ions is 3.27 *10^-3 mol dm^-3. Determine the solubility constant at this temperature.

Accepted Answer

The solubility product constant (Ksp) for copper (II) iodate, Cu(IO3)2, can be calculated using the equilibrium concentration of copper ions. Given that the formula of copper (II) iodate suggests for every mole of Cu(IO3)2 that dissolves, 1 mole of Cu2+ ions and 2 moles of IO3- ions are produced. If the equilibrium concentration of Cu2+ is 3.27×10^-3 mol dm^-3, then the concentration of IO3- ions would be twice that, or 6.54×10^-3 mol dm^-3. The Ksp can be calculated as [Cu2+][IO3-]^2 = (3.27×10^-3)(6.54×10^-3)^2 = 1.40×10^-7.

Question 19

Estimate the solubility of copper (I) chloride, CuCl, in a 0.10 mol dm^-3 solution of sodium chloride, NaCl, at a temperature of 298 K. The solubility of copper (I) chloride in water is 1.0 * 10^-3 mol dm^-3 at this temperature.

Accepted Answer

The presence of a common ion (Cl-) from NaCl will decrease the solubility of CuCl due to the common ion effect, leading to a lower solubility than in pure water.

Question 20

One drop, 0.200 cm³, of 1.00 mol dm^-3 of aqueous sodium hydroxide, NaOH, solution, is added to 25.0 cm³ of a phosphate buffer that is 0.040 mol dm^-3 in KH₂PO₄(aq) and 0.020 mol dm⁻³ in K₂HPO₄(aq). Calculate the resulting pH of the solution given that the second acid dissociation constant, pK_a2, for phosphoric acid is 7.21.

Accepted Answer

The answer of One drop, 0.200 cm³, of 1.00 mol...

Quiz 5: Chemical Change

The standard Gibbs energy of reaction for the equilibrium 2 NO₂(g) ∏ N₂O₄(g) Is -4.73 kJ mol^-1 at 298 K. Calculate the value of the equilibrium constant at this temperature.

The equilibrium constant for the reaction H₂(g) + Br₂(g) ∏ 2 HBr(g) Is 2.1 *10⁹ at 298 K. What is the value of the equilibrium constant for the reaction ½ H₂(g) + ½ Br₂(g) ∏ HBr(g) at this temperature?

The value of the equilibrium constant for the electrochemical reaction MnO₄^-(aq) + 2 H⁺(aq) + ½ Cl₂(g) ∏ Mn²⁺(aq) + ClO₃^-(aq) + H₂O(aq) Is 5.88 *10^-5. What is the value of the equilibrium constant for the reverse reaction?

When lead (II) oxide, PbO, is allowed to react with oxygen, O₂, at a temperature of 823 K and standard pressure through the reaction PbO(s) + ½O₂(g) ∏ PbO₂(s) The partial pressure of oxygen at equilibrium is 11.6 Pa. Determine the standard Gibbs energy of reaction at this temperature.

The value of the equilibrium constant for the gas-phase reaction 2 NOCl(g) ∏ 2 NO(g) + Cl₂(g) Is K = 7.65 * 10^-8 at 298.15 K. Determine the value of the equilibrium constant expressed in terms of concentrations, K_c, at this temperature.

The value of the equilibrium constant for the reaction C₂H₄(g) + H₂O(g) ∏ C₂H₅OH(g) Is 9.920 at 423 K and 6.397 at 523 K. Determine the average value of the standard enthalpy of reaction over this temperature range.

Calculate the concentration of hydronium, H₃O⁺, ions in a solution of pH = 11.2.

The pK_a of 2-chloropropanoic acid, CH₃CHClCO₂H, is 2.83. Calculate the Gibbs energy for the dissociation CH₃CHClCO₂H(aq) + H₂O(aq) ⇌ CH₃CHClCO₂^-(aq) + H₃O⁺(aq) At a temperature of 298 K.

The concentration of OH^- ions in a solution is 5.62 mmol dm^-3. Determine the pH of the solution.

The pK_b of the base cyclohexamine, C₆H₁₁NH₂, is 3.36. What is the pK_a of the conjugate acid, C₆H₁₁NH₃⁺?

Determine the pH of an aqueous solution of benzoic acid, C₆H₅COOH, of concentration 0.064 mol dm^-3. The pK_a of benzoic acid is 4.19.

Calculate the pH of an aqueous solution of sodium hydrogenphosphite, NaHPO₃. For phosphorous acid, H₂PO₃, pK_a1 = 2.00 and pK_a2 = 6.59.

Calculate the pH of a solution produced by mixing 4.3 cm³ of 0.100 mol dm^-3 potassium hydroxide, KOH, solution to 50.0 cm³ of 0.136 mol dm^-3 propanoic acid, C₂H₅COOH, solution. The pK_a of propanoic acid is 4.87.

When an excess of copper (II) iodate, Cu(IO₃) ₂, is added to water at 298 K, the equilibrium concentration of copper ions is 3.27 *10^-3 mol dm^-3. Determine the solubility constant at this temperature.

Estimate the solubility of copper (I) chloride, CuCl, in a 0.10 mol dm^-3 solution of sodium chloride, NaCl, at a temperature of 298 K. The solubility of copper (I) chloride in water is 1.0 * 10^-3 mol dm^-3 at this temperature.

Quiz 5: Chemical Change

The standard Gibbs energy of reaction for the equilibrium 2 NO2(g) ∏ N2O4(g) Is -4.73 kJ mol-1 at 298 K. Calculate the value of the equilibrium constant at this temperature.

The equilibrium constant for the reaction H2(g) + Br2(g) ∏ 2 HBr(g) Is 2.1 *109 at 298 K. What is the value of the equilibrium constant for the reaction ½ H2(g) + ½ Br2(g) ∏ HBr(g) at this temperature?

The value of the equilibrium constant for the electrochemical reaction MnO4-(aq) + 2 H+(aq) + ½ Cl2(g) ∏ Mn2+(aq) + ClO3-(aq) + H2O(aq) Is 5.88 *10-5. What is the value of the equilibrium constant for the reverse reaction?

When lead (II) oxide, PbO, is allowed to react with oxygen, O2, at a temperature of 823 K and standard pressure through the reaction PbO(s) + ½O2(g) ∏ PbO2(s) The partial pressure of oxygen at equilibrium is 11.6 Pa. Determine the standard Gibbs energy of reaction at this temperature.

The value of the equilibrium constant for the gas-phase reaction 2 NOCl(g) ∏ 2 NO(g) + Cl2(g) Is K = 7.65 * 10-8 at 298.15 K. Determine the value of the equilibrium constant expressed in terms of concentrations, Kc, at this temperature.

The value of the equilibrium constant for the reaction C2H4(g) + H2O(g) ∏ C2H5OH(g) Is 9.920 at 423 K and 6.397 at 523 K. Determine the average value of the standard enthalpy of reaction over this temperature range.

Calculate the concentration of hydronium, H3O+, ions in a solution of pH = 11.2.

The pKa of 2-chloropropanoic acid, CH3CHClCO2H, is 2.83. Calculate the Gibbs energy for the dissociation CH3CHClCO2H(aq) + H2O(aq) ⇌ CH3CHClCO2-(aq) + H3O+(aq) At a temperature of 298 K.

The concentration of OH- ions in a solution is 5.62 mmol dm-3. Determine the pH of the solution.

The pKb of the base cyclohexamine, C6H11NH2, is 3.36. What is the pKa of the conjugate acid, C6H11NH3+?

Determine the pH of an aqueous solution of benzoic acid, C6H5COOH, of concentration 0.064 mol dm-3. The pKa of benzoic acid is 4.19.

Calculate the pH of an aqueous solution of sodium hydrogenphosphite, NaHPO3. For phosphorous acid, H2PO3, pKa1 = 2.00 and pKa2 = 6.59.

Calculate the pH of a solution produced by mixing 4.3 cm3 of 0.100 mol dm-3 potassium hydroxide, KOH, solution to 50.0 cm3 of 0.136 mol dm-3 propanoic acid, C2H5COOH, solution. The pKa of propanoic acid is 4.87.

When an excess of copper (II) iodate, Cu(IO3) 2, is added to water at 298 K, the equilibrium concentration of copper ions is 3.27 *10-3 mol dm-3. Determine the solubility constant at this temperature.

Estimate the solubility of copper (I) chloride, CuCl, in a 0.10 mol dm-3 solution of sodium chloride, NaCl, at a temperature of 298 K. The solubility of copper (I) chloride in water is 1.0 * 10-3 mol dm-3 at this temperature.

The standard Gibbs energy of reaction for the equilibrium 2 NO₂(g) ∏ N₂O₄(g) Is -4.73 kJ mol^-1 at 298 K. Calculate the value of the equilibrium constant at this temperature.

The equilibrium constant for the reaction H₂(g) + Br₂(g) ∏ 2 HBr(g) Is 2.1 *10⁹ at 298 K. What is the value of the equilibrium constant for the reaction ½ H₂(g) + ½ Br₂(g) ∏ HBr(g) at this temperature?

The value of the equilibrium constant for the electrochemical reaction MnO₄^-(aq) + 2 H⁺(aq) + ½ Cl₂(g) ∏ Mn²⁺(aq) + ClO₃^-(aq) + H₂O(aq) Is 5.88 *10^-5. What is the value of the equilibrium constant for the reverse reaction?

When lead (II) oxide, PbO, is allowed to react with oxygen, O₂, at a temperature of 823 K and standard pressure through the reaction PbO(s) + ½O₂(g) ∏ PbO₂(s) The partial pressure of oxygen at equilibrium is 11.6 Pa. Determine the standard Gibbs energy of reaction at this temperature.

The value of the equilibrium constant for the gas-phase reaction 2 NOCl(g) ∏ 2 NO(g) + Cl₂(g) Is K = 7.65 * 10^-8 at 298.15 K. Determine the value of the equilibrium constant expressed in terms of concentrations, K_c, at this temperature.

The value of the equilibrium constant for the reaction C₂H₄(g) + H₂O(g) ∏ C₂H₅OH(g) Is 9.920 at 423 K and 6.397 at 523 K. Determine the average value of the standard enthalpy of reaction over this temperature range.

Calculate the concentration of hydronium, H₃O⁺, ions in a solution of pH = 11.2.

The pK_a of 2-chloropropanoic acid, CH₃CHClCO₂H, is 2.83. Calculate the Gibbs energy for the dissociation CH₃CHClCO₂H(aq) + H₂O(aq) ⇌ CH₃CHClCO₂^-(aq) + H₃O⁺(aq) At a temperature of 298 K.

The concentration of OH^- ions in a solution is 5.62 mmol dm^-3. Determine the pH of the solution.

The pK_b of the base cyclohexamine, C₆H₁₁NH₂, is 3.36. What is the pK_a of the conjugate acid, C₆H₁₁NH₃⁺?

Determine the pH of an aqueous solution of benzoic acid, C₆H₅COOH, of concentration 0.064 mol dm^-3. The pK_a of benzoic acid is 4.19.

Calculate the pH of an aqueous solution of sodium hydrogenphosphite, NaHPO₃. For phosphorous acid, H₂PO₃, pK_a1 = 2.00 and pK_a2 = 6.59.

Calculate the pH of a solution produced by mixing 4.3 cm³ of 0.100 mol dm^-3 potassium hydroxide, KOH, solution to 50.0 cm³ of 0.136 mol dm^-3 propanoic acid, C₂H₅COOH, solution. The pK_a of propanoic acid is 4.87.

When an excess of copper (II) iodate, Cu(IO₃) ₂, is added to water at 298 K, the equilibrium concentration of copper ions is 3.27 *10^-3 mol dm^-3. Determine the solubility constant at this temperature.

Estimate the solubility of copper (I) chloride, CuCl, in a 0.10 mol dm^-3 solution of sodium chloride, NaCl, at a temperature of 298 K. The solubility of copper (I) chloride in water is 1.0 * 10^-3 mol dm^-3 at this temperature.