Question

In: Chemistry

When spheres of radius r are packed in a simple cubic arrangement, they occupy 52.0 %...

When spheres of radius r are packed in a simple cubic arrangement, they occupy 52.0 % of the available volume. Use the fraction of occupied volume to calculate the value of a, the length of the edge of the cube in terms of r.

Solutions

Expert Solution

In a simple cubic arrangement, the vertices of the cube coincides with the center of the spheres.

There are 8 spheres on the 8 vertices of the cube. Hence, only 1/8 th of each sphere lies inside the cube.

Volume of each sphere of radius r is   .

Hence, 1/8 the of the volume of 8 spheres that lies inside the cube must equal the volume of 1 complete sphere.

Hence, the volume of all the spheres that lies inside the cube must be .

Now, the volume of the cube with edge length a is .

It is given that only 52% of the cube is occupied by the spheres.

Hence,

We can easily solve for the edge length a in terms of r from the above relation as shown below.

Hence, the relation between the edge length a and radius of sphere r is .


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