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The reaction between EXCESS dilute hydrochloric acid and sodium thiosulphate is used to investigate factors that influence reaction rate - NSC Physical Sciences - Question 5 - 2023 - Paper 2
Question 5
The reaction between EXCESS dilute hydrochloric acid and sodium thiosulphate is used to investigate factors that influence reaction rate. Na₂S₂O₃(aq) + 2HCl(aq) → 2... show full transcript
Worked Solution & Example Answer:The reaction between EXCESS dilute hydrochloric acid and sodium thiosulphate is used to investigate factors that influence reaction rate - NSC Physical Sciences - Question 5 - 2023 - Paper 2
Step 1
Define reaction rate.
Answer
The reaction rate can be defined as the change in concentration of products or reactants per unit time. It can be expressed as:
Rate = [\text{Rate} = \frac{\Delta [C]}{\Delta t}] where (\Delta [C]) is the change in concentration and (\Delta t) is the change in time.
Step 2
Step 3
Calculate the value of P in the table.
Answer
To find P, we need to maintain consistency in the concentration calculations. From runs 2 and 3, we can use the average concentration formula:
- The concentration is given by: [\text{Concentration} = \frac{\text{moles}}{\text{volume (in dm}^3\text{)}}]
- From Run 2: Concentration = 0.10 mol·dm⁻³ Volume = 40 cm³ or 0.04 dm³ Thus, moles of Na₂S₂O₃ = 0.10 mol·dm⁻³ × 0.04 dm³ = 0.004 moles.
- Run 3 has 20 cm³ = 0.02 dm³. Therefore: [ P = \frac{0.004\text{ moles}}{0.02 \text{ dm}^3} = 0.20 \text{ mol·dm}^{-3}]
Step 4
Calculate the average reaction rate with respect to sodium thiosulphate, Na₂S₂O₃(aq), in g·s⁻¹.
Answer
Given that 0.21 g of sulphur is produced when the cross vanishes, the molar mass of Na₂S₂O₃ is needed to find the change in moles. The calculation is as follows:
- Molar mass of Na₂S₂O₃ is approximately 158 g/mol.
- Number of moles = ( n = \frac{m}{M} = \frac{0.21g}{158g/mol} \approx 0.00133 ) moles.
- Average reaction rate = ( \frac{0.00133\text{ moles}}{20.4 s} \approx 0.000065\text{ moles/s} \approx 0.01 ext{ g/s} ).
Step 5
Sketch the Maxwell-Boltzmann distribution curve for the reaction at 20 °C. Label this curve as A.
Answer
When sketching the Maxwell-Boltzmann distribution, the x-axis represents kinetic energy, while the y-axis represents the number of particles. Curve A should show a peak that represents the energy distribution at 20 °C.
Curve B, which represents a higher temperature of 35 °C, will shift to the right and will have a higher peak, indicating that more particles have higher energy, which contributes to a greater frequency of effective collisions.
Step 6
Explain the effect of temperature on reaction rate in terms of the collision theory.
Answer
As temperature increases, the kinetic energy of the particles also increases. This results in:
- More particles moving faster, which correlates to having higher kinetic energy.
- Increased frequency of collisions, as particles collide more often per unit of time.
- More effective collisions per unit of time, as a greater proportion of the particles possess enough energy to overcome the activation energy barrier required for the reaction. Overall, this leads to an increased reaction rate.