Polycarbonate plastic has a density of 1.2 g/cm3. A photo frame is constructed from
two 5.2 mm sheets of polycarbonate. Each
sheet measures 22 cm by 20 cm.
What is the mass of the photo frame?

The mass of the photo frame : = 549.12 g

Given

a photo frame

two 5.2 mm sheets = 0.52 cm

22 cm by 20 cm dimension

Required

the mass

Solution

The volume of one sheet = l x w x h

= 22 cm x 20 cm x 0.52 cm

= 228.8 cm³

Mass of one sheet :

= density x volume

= 1.2 g/cm³ x 228.8 cm³

= 274.56 g

So for two sheets of polycarbonate :

= 2 x  274.56 g

= 549.12 g

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

since electrons are negative the answer is neagtaive