Look at the diagram below.

the diagram on the left represents the diagram on the right represents
a.
the specific heat of a system; the heat of vaporization of a liquid
b.
the release of heat by a system; the absorption of heat by a system
c.
the absorption of heat by a system; the release of heat by a system
d.
the heat of vaporization of a liquid; the specific heat of a system

So the one with the arrow going IN to the cylinder will be an absorption of heat. The arrow going outwards will be a release of heat

Explanation:

6.4 cm (max) - 25 cm (min)

> b takes place in the gas phase in an isothermal tubular reactor. the feed is one mole of a per one mole of c, an inert. the entering temperature and pressure are 427°c and 10 atm, respectively. the gas constant r = 0.08206 atm · l/mol · k.