A mixture of gaseous reactants is put into a cylinder, where a chemical reaction

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 251.kJ of work on the piston during the reaction. Is the reaction exothermic or endothermic? Does the temperature of the water bathe go up or down? Does the pisto move in or out? Does the reaction abosrb or release energy? How much energy does the reaction release or absorb in KJ? 137.kJ of heat flows into the system during the reaction. The position of the piston is also monitored, and it is determined from this data that the system does 1 atm . The cylinder is also submerged in a large insulated water bath. (See sketch at right.) The temperature of the water bath is monitored, and it is determined from this data that

Explanation / Answer

Is the reaction exothermic or endothermic?

The reaction is endothermic because heat is absorbed by the system. Heat flows from water bath to the system through walls of vessel.

Does the temperature of the water bathe go up or down?

The temperature of the water bathe go down as heat flows from water to the system through reaction vessel.

Does the pisto move in or out?

The piston moves out as the work is done on the piston by the system during the reaction.

Does the reaction abosrb or release energy?

The reaction releases energy as heat absorbed is less than work done. The difference between heat absorbed and work done is negative which means energy is lost by the system or in other words energy is released by system.

How much energy does the reaction release or absorb in KJ?

The energy released is the difference between heat absorbed and work done = 137 kJ - 251 kJ = -114 kJ   Here negative sign signifies release of energy.

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