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7. (a) Define the rate of a chemical reaction - Leaving Cert Chemistry - Question 7 - 2013
Question 7
7. (a) Define the rate of a chemical reaction. (b) Explain clearly why there is an almost instantaneous reaction between aqueous solutions of sodium chloride and si... show full transcript
Worked Solution & Example Answer:7. (a) Define the rate of a chemical reaction - Leaving Cert Chemistry - Question 7 - 2013
Step 1
Step 2
Explain clearly why there is an almost instantaneous reaction between aqueous solutions of sodium chloride and silver nitrate.
Answer
The reaction between sodium chloride (NaCl) and silver nitrate (AgNO₃) is almost instantaneous because both compounds are ionic and dissociate into their constituent ions in solution. This leads to the formation of silver chloride (AgCl), which precipitates out quickly. The ions are mobile and can collide immediately to form the precipitate, resulting in a rapid reaction.
Step 3
Suggest two ways to increase the rate of this reaction.
Answer
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Increase Pressure: If the reaction involves gases, increasing the pressure will lead to more collisions between reactant molecules. More collisions increase the rate of reaction.
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Use a Catalyst: Adding a catalyst lowers the activation energy required for the reaction, allowing more molecules to participate in the reaction in a given time.
Step 4
Describe how you would measure the reaction time when 10 cm³ of 1.0 M hydrochloric acid solution and 50 cm³ of 0.20 M sodium thiosulfate solution react according to the following balanced equation.
Answer
To measure the reaction time, place the sodium thiosulfate solution in a noticeable container and add the hydrochloric acid solution quickly. Start a stopwatch as soon as the hydrochloric acid is added. Observe the mixture for the change in color to a cloudy yellow, which indicates the formation of sulfur. Stop the timer as soon as the solution becomes opaque, noting the time taken for the reaction to occur.
Step 5
Draw a reaction profile diagram for an exothermic reaction indicating clearly on your diagram (i) the activation energy (Ea) for the reaction, (ii) the heat of reaction (ΔHr).
Answer
In an exothermic reaction diagram, the reactants are at a higher energy level compared to the products. The activation energy (Ea) is depicted as the peak energy barrier that must be overcome for the reaction to occur. The heat of reaction (ΔHr) is the difference in energy between the reactants and the products, and it is represented by a downward shift in the energy level of the products relative to the reactants.
- Label the y-axis as 'Energy' and the x-axis as 'Reaction Progress'.
- Clearly mark and annotate Ea and ΔHr on the diagram.