In heterogeneous catalysis the rate of the catalyzed reaction, k obs , depends o
ID: 591673 • Letter: I
Question
In heterogeneous catalysis the rate of the catalyzed reaction, kobs, depends on the contact surface area between the reactants in one phase and the catalyst in another phase.
Suppose you have a block of platinum measuring 2.41 cm × 2.98 cm × 2.58 cm. Platinum has a density of 21.45 g/cm3.
(a) What is the total surface area, i.e. the area in possible contact with the reactants, of this block of platinum?
__________cm2
(b) What is the volume of the block?
__________ cm3
(c) What is the mass of the block?
________ g
(d) What is the accessible surface area per unit of mass?
_________ cm2/g
Metal catalysts are often added to a reaction powdered or adsorbed to a carrier, such as graphite or silica, to increase their contact surface area.
Suppose you figure out a process that whittles the block of platinum down to a homogeneous collection of spheres with a diameter of 336 nm.
(e) What is the surface area of one such sphere?
_________ cm2
(f) What is the mass of one such sphere?
__________g
(g) Assuming you have the exact same mass of spheres as the block you started with, how many spheres do you have?
__________ spheres
(h) What is the total surface area, i.e. the area in possible contact with the reactants, of this batch of platinum spheres?
_________cm2
(i) What is the accessible surface area per unit of mass?
_________ cm2/g
(j) What is the approximate fold-increase in reaction rate that can be obtained by using these spheres instead of the block of platinum?
_________fold
Explanation / Answer
a) it is a cuboid surface area =2(lb+lh+bh), hence answer = 42.176 cm2
b) volume = 2.41 x 2.98 x 2.58 = 18.53 cm3
c) mass = density x volume = 21.45 x 2.41x 2.98 x 2.58 = 397.44 gm
d) surface area / mass =0.106 cm2 /gm