Methanol and hydrochloric acid react according to the following balanced equation: CH₃OH(aq) + HCl(aq) → CH₃Cl(aq) + H₂O(l) 5.1 State TWO factors that can INCREASE the rate of this reaction - NSC Physical Sciences - Question 5 - 2016 - Paper 2

The reaction rate is defined as the change in concentration of a reactant or product over time. It reflects how quickly reactants are converted into products in a chemical reaction.

To calculate the average reaction rate, we use the formula:

ext{Average Rate} = -rac{ ext{Change in Concentration}}{ ext{Time}}

From the data:

• Initial concentration at 0 minutes = 1.90 mol dm⁻³
• Final concentration at 15 minutes = 1.45 mol dm⁻³

Change in concentration = 1.45 - 1.90 = -0.45 mol dm⁻³.

Time interval = 15 minutes.

Now substituting into the formula:

ext{Average Rate} = -rac{-0.45 ext{ mol dm}^{-3}}{15 ext{ min}} = 0.03 ext{ (mol dm}^{-3} ext{ min}^{-1})

To graph the data, plot the time (in minutes) on the x-axis and the concentration of HCl (in mol dm⁻³) on the y-axis. The points to plot are:

• (0, 1.90)
• (15, 1.45)
• (210, 0.60)

Since the graph is not a straight line, ensure that the curve reflects the decreasing concentration of HCl over time.

To estimate the concentration of HCl at the 40th minute, observe the trend in the graph. The graph should be used to interpolate between the data points. Given the decreasing concentration, the concentration of HCl at 40 minutes could be approximated around 1.20 mol dm⁻³ based on the curve drawn.

At the 215th minute, the concentration of CH₃Cl can be approximated as follows:

Let’s say the concentration at the 215th minute worked out to be roughly 0.60 mol dm⁻³.

The volume of the solution = 60 cm³ = 0.060 dm³.

Using the formula:

$ext{Mass} = ext{Concentration} imes ext{Volume} imes ext{Molar Mass}$

where Molar Mass of CH₃Cl = 50.5 g/mol:

$ext{Mass} = 0.60 ext{ mol dm}^{-3} imes 0.060 ext{ dm}^{3} imes 50.5 ext{ g/mol} = 1.81 ext{ grams}$.