Under acidic conditions, iodine undergoes a substitution reaction with propanone. $\text{CH}_3\text{COCH}_3(\text{aq}) + \text{I}_2(\text{aq}) \rightarrow \text{CH}_3\text{COCH}_2\text{I}(\text{aq}) + \text{HI}(\text{aq})$ The rate of this reaction is studied with a colorimeter. As the $\text{I}_2$ is consumed, the yellow/brown colour of the $\text{I}_2(\text{aq})$ solution becomes colourless, so the absorbance of the mixture changes. A calibration curve graph is produced from solutions of known $\text{I}_2(\text{aq})$ concentrations, and the absorbance is recorded while the reaction continues. What is the rate of reaction at $20\,\text{s}$?
- A$5 \times 10^{-6}\,\text{mol dm}^{-3}\,\text{s}^{-1}$
- B$1 \times 10^{-5}\,\text{mol dm}^{-3}\,\text{s}^{-1}$
- C$5 \times 10^{-3}\,\text{mol dm}^{-3}\,\text{s}^{-1}$
- D$1 \times 10^{-2}\,\text{mol dm}^{-3}\,\text{s}^{-1}$