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 1atm . 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 336.kJ of energy. The temperature of the water bath is monitored, and it is determined from this data that 136.kJ of heat flows out of the system during the reaction. Is the reaction exothermic or endothermic?exothermicendothermicDoes the temperature of the water bath go up or down?updownneitherDoes the piston move in or out?inoutneitherDoes the gas mixture do work, or is work done on it?does workwork is done on itneitherHow much work is done on (or by) the gas mixture? Round your answer to 3 significant digits. kJ

Answer 1

Answer: (a) Exothermic

              (b) Temperature of the water bath goes up

Explanation:

As the heat flow out of the system it will have a negative value therefore leading to the conclusion that it is an exothermic reaction.

Exothermic reactions represents the release of the heat energy out of the system which therefore means the temperature of the water in the water bath tends to rise up as well.

The system is doing work on the piston as it will move upwards which means that the work is done by system leading its sign to be negative.

$E = Q + W\\-336 = -Q -W \\-336 = -136-W\\W= 200 KJ$

Answer 2

Answer:

Pleae see below

Explanation:

According to the first law of thermodynamics the change in energy, ΔE , in a system is equal to:

ΔE = q + w

where q is the heat flow involved, and w is the work done on or by the system.

If q flows out of the system, it is negative.

If q flows in from the surroundings into the system, it is positve.

If work is done by the system, it is negative.

If work is done on thesystem, it is positve.

Wr are told that in this chemical reaction 336 kJ are released, thus

ΔE = -336 kJ

The negative sign arises from the fact that the energy is released, i.e.exothermic reaction.

We are also told that 136 kJ of heat flows out of the system, therefore

q = - 136 kJ

The value of q is negative because heat flows out of the system into the water bath.

So we have the following equation:

ΔE = q+w

-336 kJ = - 136 kJ + w

w = -336 kJ + 136 kJ = - 200 kJ

With this in mind, lets answer our questions:

Is the reaction exothermic or endothermic?

The reaction is exothermic, we know 336 kJ of energy are released as stated in the question.

Does the temperature of the water go up or down.

Since the reaction releases energy, and from the fact that as stated heat flows out of the system, the water temperature goes up.

Does the piston move in or out?

The  piston moves out since our work is negative ( - 200 kJ) and work against a constant external pressure, as stated in the question is by definition:

w =  - pΔV    ⇒ ΔV = Vf - Vi must be positive for the overall work to be

-200 kJ as calculated and the piston therefore has moved out.

Does work is done on (by) ?

Remember the extenal pressure is constant, and the piston has moved out  so the gas reaction does work of expansion, and the work is done by the system.

How much work is done on (or) by the gas mixture?

As calculated prevoiusly, the work done by the gas mixture is 200 kJ

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