Question

Propanoic acid to propenoic acid

Answer 1

Step 1 By H V Z reaction propanoic acid is converted to alpha chloro or bromo or iodo propanoic acid .

Step 2 alpha chloro or bromo or iodo propanoic acid is treated with alcoholic KOH(in ethanol) followed by acidification alpha chloro or bromo or iodo propanoic acid is formed

Answer 2

The conversion is :

Both propenoic acid and propionic acid are 3 carbon acids, the only difference is that propenoic acid has a double bond 

Propenoic acid (CH2CHCOOH) 
Propionic acid (CH3CH2COOH) 

Therefore you need to add hydrogen across the double bond to form the saturated propionic acid.