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Chloroethane decomposes when heated according to the balanced equation: C2H5Cl(g) → C2H4(g) + HCl(g) The following data were obtained at a certain temperature T for the decomposition of the chloroethane and the formation of the hydrogen chloride during this reaction - Leaving Cert Chemistry - Question b - 2021
Question b
Chloroethane decomposes when heated according to the balanced equation: C2H5Cl(g) → C2H4(g) + HCl(g) The following data were obtained at a certain temperature T fo... show full transcript
Worked Solution & Example Answer:Chloroethane decomposes when heated according to the balanced equation: C2H5Cl(g) → C2H4(g) + HCl(g) The following data were obtained at a certain temperature T for the decomposition of the chloroethane and the formation of the hydrogen chloride during this reaction - Leaving Cert Chemistry - Question b - 2021
Step 1
Define rate of a reaction.
Answer
The rate of a reaction is defined as the change in concentration of a reactant or product per unit time. Mathematically, it can be expressed as:
ext{Rate} = rac{- ext{d}[C_2H_5Cl]}{ ext{dt}} = rac{ ext{d}[HCl]}{ ext{dt}}Where [C2H5Cl] is the concentration of chloroethane and [HCl] is the concentration of hydrogen chloride.
Step 2
Use the data given to plot, on the same sheet of graph paper and using the same set of axes, curves to compare the changes in concentration of the chloroethane and the hydrogen chloride with time.
Answer
-
Axes Setup: Label the x-axis as 'Time (s)' and the y-axis as 'Concentration (M)'. Make sure the scale is appropriate for the data.
-
Plotting Points:
- For C2H5Cl:
- (0, 2.00)
- (80, 1.02)
- (160, 0.52)
- (320, 0.13)
- For HCl:
- (0, 0.98)
- (80, 1.48)
- (160, 1.87)
- For C2H5Cl:
-
Drawing Curves: Draw smooth curves through the points for both concentrations, ensuring the curves accurately represent the data. Include a point at each of the plotted times.
Step 3
Find the instantaneous rate of HCl formation (in M s⁻¹) at 120 s.
Answer
To find the instantaneous rate of HCl formation at 120 s, we will take the slope of the tangent line at that point on the HCl concentration curve:
-
Identify the two points around 120 s:
- At 100 s, approximately 1.20 M
- At 140 s, approximately 1.78 M
-
Calculate the slope (rise/run):
- Rise = 1.78 - 1.20 = 0.58 M
- Run = 140 s - 100 s = 40 s
-
Instantaneous rate:
ext{Rate} = rac{0.58}{40} = 0.0145 ext{ M s}^{-1}
Thus, the instantaneous rate of HCl formation at 120 s is approximately 0.0145 M s⁻¹.