Would the carbon atoms in a molecule such as stearic acid actually be expected to form a linear chain?

Answer 1

No, for two reasons. Stearic acid is a chain of 18 carbons, each attached to two hydrogens, except -COOH at one end and CH3 at the other. The C-C-C angle, C^C, is 107deg. So the straightest it could get would be a zigzag. Second, in solution, the zigzag chain would be flexible and form a broad, shallow letter C- or S-shape.