Passage IV
Chemical reaction that release heat areexothermic reactions. The amount of heat released depends on the number of moles of reactants consumed in the reaction. A mole of any substance is 6 × 1023 molecules or formula units of the substance.
When sodium hypochlorite (NaCIO) and sodium iodide (NaI) are dissolved in acidic H2O, an exothermic reaction occurs
NaCIO + NaI → products + heat
Students did an experiment to study this reaction.
Experiment
In each of 8 trails, the students performed Steps 1-5:
1. A known volume of a 0.2 mole/L aqueous NaCIO solution was poured into a foam coffee cup. A lid was placed on the cup.
2. A thermometer was placed into the solution through a hole in the lid. The solution's initial temperature, Ti, of 22.0° C was recorded.
3. The lid was lifted, and a known volume of a 0.2 mole/L aqueous NaI solution, also at a Ti of 22.0°C, was poured into the cup. The lid was put back on the cup, and the solution was swirled.
4. The solution's final (maximum) temperature, Tf was measured.
5. The change in temperature, △T, was calculated :
△T= Tf - Ti
The data for each trail are shown in Table 1.
The students plotted △T versus the volume of NaCIO solution for each trail (see Figure 1).
Then they identified the trial for which △T had its greatest value. The ratio of volume of the NaCIO solution to the volume of the NaI solution for this trial is the mole ratio for the reaction.
25. Suppose a trial had been performed with 20 mL of NaCIO solution and 80 mL of NaI solution. Based on Figure 1, △T for this new trial would most likely have been closest to which of the following?
Your Answer is
Correct Answer is B
Explanation
The volume of NaClO given in the question is 80 mL, and the volume of NaI is 20 mL. The situation is between Trail 2 and Trail 2. So △T should be between 0-3.5°C, option B is within this range.