Which of the following would introduce the greatest increase in the rate of the chemical reaction above?
A. An increase in temperature and a decrease in the concentration of the reactants.
B. A decrease in volume and an increase in the pressure of the reactants.
C. A decrease in temperature and an increase in the concentration of the reactants.
D. An increase in temperature and an increase in the concentration of the reactants.
Generally, an increase in the concentration of reactants increases the rate of reaction, this is because more ions will have larger surface area and collision opportunities leading to reactions at lesser time.
Increase in temperature also increases the rate of chemical reactions, this is because at higher temperatures, more particles and ions will acquire more energy to collide at faster rate leading to increased reaction rate.
Now for the right answer to the above question:
- Option A is incorrect. a decrease in the concentration of the reactants will decrease the rate of collision, thereby increasing the time taken to complete the reaction.
- Option B is incorrect. the reactants are not in gaseous form, therefore change in volume and pressure will have no effect on the rate of reaction.
- C is incorrect. a decrease in the temperature of the reactants will lower the energy of collision thereby reducing the reaction rate.
- D is the correct answer. Increase in the concentration and temperature of reactants generally increases the collision rate, and therefore will increase the rate of chemical reactions.
You may please note these/this:
- For a closed reversible reaction, the effect of temperature change will depend on whether the overall reaction is exothermic or endothermic. But the reaction in this question is shown as non-reversible, and generally, application of more heat on reactants will cause a more vigorous reaction.
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/ culled from 2017 JAMB-UTME Chemistry question 38 /