Question

Factors affecting reaction rates

1) In the presence of a strong acid, permanganate ion reacts with oxalic acid according to the following net ionic equation: 2MnO?4(aq)+5H2C2O4(aq)+6H+(aq)?10CO2(g)+2Mn+2(aq)+8H2O(l). Which of the following permanganate solutions will have the fastest reaction rate?

Answers

a. 4.01 g of KMnO4 dissolved in 2L of 1.0N H2SO4

b. 2.10 g of KMnO4 dissolved in 500mL of 1.0N H2SO4

c. 7.25 g of KMnO4 dissolved in 2000mL of 1.0N H2SO4

d. 4.21 g of KMnO4 dissolved in 0.750L of 1.0N H2SO4

2) For a reaction between two immiscible liquids, shaking the container may speed up the reaction because:

Answers

a. shaking does not add energy to the reaction mixture.

b. shaking mixes the liquids, breaking the liquids up into smaller portions, increasing surface area, and thus increasing the rate of reaction.

c. shaking makes the molecules of the liquids move more quickly.

d. shaking increases the rate of reaction by allowing air to mix with the liquids, and air catalyzes the reaction.

3) Assume the rate of a reaction doubles with each 10?C increase in temperature. By how much would the rate increase if the temperature is increased by 40?C?

Answers

a. twice

b. four times

c. eight times

d. sixteen times

4) In general, a mixture of gaseous reactants can be expected to react at a faster rate than powdered solid reactants because:

Answers

a. gases mix more thoroughly than do the solids, increasing the chance of collision between reactants.

b. solids have a higher kinetic energy than gases.

c. gases have less space between atoms and molecules and so they will react faster.

d. None of the above

Answer 1

1 Ans. One of the factors on which rate of a reaction depends is the concentration of the reactants. In all the options given, the concentration of H₂SO₄ which act as catalyst is the same.

FInd out the concentrations of MnO₄^- in all cases.

The net ionic equation is

Option (a)

Mass of KMnO₄ = 4.01g

No. of mol of KMnO₄ is

This no. of mol is present in 2L solution of KMnO₄ and H₂SO₄.

Concentration of MnO₄^- is

Similarly, the concentration of MnO₄^- can be calculated in all cases.

Option	No. of mol of MnO4-	Vol. of solution (L)	Conc. of MnO4- (in mol/L)
a	0.0254	2	0.0127
b	0.0133	0.5	0.0266
c	0.0459	2	0.0230
d	0.0266	0.750	0.0355

The concentration of MnO₄^- is the largest in option (d). So, the rate of the reaction will be the fastest in option (d).

2 Ans. For a reaction between two immiscible liquids, shaking increases the rate of the reaction because shaking breaks down the liquid into smaller portions which increase the surface area and there is increase in interactions. So, the correct option is (b).

3 Ans. The rate of a reaction doubles with each 10^oC  rise in temperature. So, when the temperature in increased by 40^oC, the rate of the reaction will increase by 2x2x2x2 = 16. Therefore, the rate will be 16 times its initial rate.

4 Ans. Mixture of gaseous reactants react faster than solids because in gaseous state, the reactants are free to move and there is higher chance of coliision between the reactants. So, the correct option is (a).