Four different flasks, A, B, C and D, at the same temperature, contain a mixture of PCl₃, PCl₅ and Cl₂. The concentration, in mol L⁻¹, of these components in each of the flasks is shown below. In three of the four flasks, the mixture of gases is at equilibrium. In which one is the mixture of gases not at equilibrium? | Flask | [PCl₃](g) | [PCl₅](g) | [Cl₂](g) | |-------|-----------|-----------|----------| | A | 0.15 | 0.20 | 0.30 | | B | 0.20 | 0.15 | 0.15 | | C | 0.10 | 0.40 | 0.40 | | D | 0.30 | 0.80 | 0.15 |

SSCE VCE Chemistry Extent of Chemical Reactions: Four different flasks, A, B, C a

Four different flasks, A, B, C and D, at the same temperature, contain a mixture of PCl₃, PCl₅ and Cl₂ - VCE - SSCE Chemistry - Question 9 - 2008 - Paper 1

Question 9

Four different flasks, A, B, C and D, at the same temperature, contain a mixture of PCl₃, PCl₅ and Cl₂. The concentration, in mol L⁻¹, of these components in each of... show full transcript

Worked Solution & Example Answer:Four different flasks, A, B, C and D, at the same temperature, contain a mixture of PCl₃, PCl₅ and Cl₂ - VCE - SSCE Chemistry - Question 9 - 2008 - Paper 1

Step 1

Identify the equilibria condition

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Answer

To determine the flask that is not at equilibrium, we first need to analyze the fundamental equilibrium expression for the chemical reaction involving PCl₃, PCl₅, and Cl₂. Assuming a general equilibrium reaction:

$PCl_3 + Cl_2 \rightleftharpoons PCl_5$

The equilibrium constant expression can be formulated as:

$K_{c} = \frac{[PCl_5]}{[PCl_3][Cl_2]}$

Step 2

Calculate $K_c$ for each flask

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Next, we calculate the value of $K_c$ for each flask using the concentrations provided:

Flask A: $K_{c} = \frac{0.20}{0.15 \times 0.30} = \frac{0.20}{0.045} \approx 4.44$

Flask B: $K_{c} = \frac{0.15}{0.20 \times 0.15} = \frac{0.15}{0.03} = 5.00$

Flask C: $K_{c} = \frac{0.40}{0.10 \times 0.40} = \frac{0.40}{0.04} = 10.00$

Flask D: $K_{c} = \frac{0.80}{0.30 \times 0.15} = \frac{0.80}{0.045} \approx 17.78$

Step 3

Determine which flask is not at equilibrium

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Answer

We compare these $K_c$ values to find anomalies. Using the ratios calculated, if any of the flasks shows a deviation from these constant values, it indicates that it is not at equilibrium. Comparing the ratios:

Flask A: 4.44
Flask B: 5.00
Flask C: 10.00
Flask D: 17.78

The least concentration of $[Cl_2]$ in Flask B indicates that the gas mixture is shifting towards producing reactants, making Flask B the mixture not at equilibrium.

Four different flasks, A, B, C and D, at the same temperature, contain a mixture of PCl₃, PCl₅ and Cl₂ - VCE - SSCE Chemistry - Question 9 - 2008 - Paper 1

Worked Solution & Example Answer:Four different flasks, A, B, C and D, at the same temperature, contain a mixture of PCl₃, PCl₅ and Cl₂ - VCE - SSCE Chemistry - Question 9 - 2008 - Paper 1

Identify the equilibria condition

Calculate $K_c$ for each flask

Determine which flask is not at equilibrium

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