Question

A mixture of gaseous reactants is put into a cylinder, where a chemical reaction turns them into gaseous products. The cylinder has a piston that moves in or out, as necessary, to keep a constant pressure on the mixture of . The cylinder is also submerged in a large insulated water bath. (See sketch at right.) From previous experiments, this chemical reaction is known to release of energy. The temperature of the water bath is monitored, and it is determined from this data that of heat flows out of the system during the reaction.

Answer 1

a)Exothermic

b) it goes up

c) The piston must move out

d)The energy is released by the system

e)ΔE = -616 kJ

Explanation:

sign convention for heat flow:

if the heat flows into the system it is marked with positive sign

when the heat flows out the system it is marked with negative sign

sign convention for work

if work is done on the system it is marked positive

if work is done by the system it is marked negative

sign convention for internal energy

if energy absorbed by system mark positive

if energy released by system mark negative

a)

the heat flow flowing out of the system (q= -300 kJ)

thus the reaction is Exothermic

b)

In exothermic reaction, heat flows from the system to surroundings.

surrounding here is water bath.

As the system is exothermic, hence the temperature of water bath goes up

c)

It is given that 316 kJ of work is done by the system, applying expansion.

To maintain constant pressure of 1 atm the decreased pressure can be compensated with an increase on volume . To increase volume the piston must move out

d)

According to 1st law of thermodynamics,

ΔE =q +w            ⇒1

here,

ΔE = q +w  

ΔE =  -300 kJ -316 kJ

ΔE = -616 kJ          ⇒2

the negative sign denotes the energy is released by the system

e)

from ΔE = -616 kJ   the amount of energy released by the reaction is ΔE = -616kJ