A mixture of gaseous reactants is put into a cylinder, where a chemical reaction
ID: 701128 • Letter: A
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 1 atm. The cylinder is also submerged in a large insulated water bath. (See sketch at right.) atm piston cylinder The temperature of the water bath is monitored, and it is determined from this data that 387. kJ of heat flows out of the system during the reaction. The position of the piston is also monitored, and it is determined from this data that the piston does 353. kJ of work on the system during the reaction water bath gases exothermic Is the reaction exothermic or endothermic? x1 O endothermic Does the temperature of the water bath go up or down? up O down neither O in out O neither o absorlb o release Does the piston move in or out? Does the reaction absorb or release energy? neither How much energy does the reaction absorb or release? Round your answer to 2 significant digits. kJExplanation / Answer
(a) Reaction is exothermic becuase it is given that 387 kJ energy is released from the system to the water bath. and work done by the piston on the system is 353 kJ which is less than the energy released . so overall the reaction is exothermic.
(b) The temperature of the water bath can go up because we are giving heat to the water and by relation dQ= mCpdT..the temperature got increased.
(c) The piston will move down as here given that work done by the piston on the system therefore from work pdV is negative that means volume of the system reduced that means pistons goes down
(d) Reaction releases the energy because heat out is greater than work in
(e) The amount of energy released = dQ-dW
= -(387) - (-353) = -34 kJ
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