the definitions of heat and work A mixture of gaseous reactants is put into a cy

Question

the definitions of heat and work A mixture of gaseous reactants is put into a cylinder, where a chemical reaction turns them into gaseous products. The 1 atm pressure linder has a piston that moves in or out, as necessary, to keep a constant pressure on the mixture of 1 atm. The cylinder is also submerged in a large insulated water bath. (See sketch at right.) the water bath is monitored, and it is determined from this data that 195, kJ of heat flows into the m The position of the piston is also monitored, and it is determined from this data that the bath system during the reaction. piston does 208-kl of work on the system during the reaction. gases Is the reaction exothermic or endothermic? endothermic Does the temperature of the water bath go updown down? neither in Does the piston move in or out? out neither absorb release neither Does the reaction absorb or release energy? Check

Explanation / Answer

Sol:

# (a) reaciore is "endothermic reaction" , because during the reaction 195 KJ heat flows into the system(i.e heat absorb by system)

ENDOTHERMIC REACTION- energy is absorb and

EXOTHERMIC REACTION- energy is evolve( release).

#(b) Temperature of the water bath goes "down" . this is because of heat always transfer from hot body to cold body ( natural process).therefore temperature of water bath decrease continuosly.

# (c) during the reaction 208J of work done on the system , therefore piston will move " in" ( compression of gas).

We know W= -Pext . V

Where W = work done , V = V2- V1 i.e change in volume .

and Pext = external pressure .

and for compression of a gas V2< V1 i.e decrease in volume and therefore piston move inside.

V2 = final volume

V1 = initial volume

# (d) as the reaction is endothermic therefore " reaction release energy".

Note:- IUPAC sign convention for heat and work:-

Heat evolve by the system is negative

Heat absorb by the system is positive

Work done on the system is positive and

Work done by the system is negative.

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