Consider this reaction: 3Fe2O3 (s) + CO (g) → 2Fe3O4 (s) + CO2 (g). Which of the following would increase the rate of the reaction? a. adding the Fe3O4 b. decreasing the temperature c. increasing the surface area of Fe2O3 d. increasing the volume of the reaction vessel

Answer;

C. increasing the surface area of Fe2O3

Explanation; The rate of reaction refers to the speed at which products are formed from reactants. The rate of any chemical reaction depends on a number of factors which include, surface area, temperature, concentration of reactants among others. When solids and liquids react, increasing the surface area of the solid will increase the rate of reaction. Thus, decrease in the size of particles causes an increase in the total surface area of the solid and therefore increasing the rate of reaction.

The balanced reaction is 3Fe₂O₃ (s) + CO (g) → 2Fe₃O₄ (s) + CO₂ (g). Rate of reaction is decrease in the concentration of reactant or increase in the concentration of product with unit time. To increase rate of any reaction either reactant concentration is to be increased. Here (a) addition of Fe₃O₄ will decrease the reaction rate, rather it facilitates the reaction to move backward direction, (b) temperature effect is not clear as it is not mentioned whether the reaction is exothermic or endothermic, (c) if surface area of Fe₂O₃ is increased then more CO molecules can react with more Fe₂O₃ molecules at a time, therefore, reaction rate will increase, (d) increase in the volume of reaction vessel will not affect rate of reaction because reactant and product both have same volume of gaseous compound CO and CO₂ respectively.

So, increase in surface area of Fe₂O₃ would increase rate of the reaction.