10 Understanding the definitions of heat and work A mixture of gaseous reactants

Question

10 Understanding 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 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.) From previous experiments, this chemical reaction is known to absorb 322. kJ of energy 1 atm pressure The position of the piston is monitored, and it is determined from this data that the system does 329. k of work on the piston during the reaction. Is the reaction exothermic or endothermic? endot up Does the temperature of the water bath go up or O down down? O neither O in out O neither O in Does the piston move in or out? ° out O neither Does heat flow into or out of the gas mixture? How much heat flows? Round your answer to significant digits

Explanation / Answer

With given data,

change in internal energy (dU) can be calculated as,

dU = q + w

here,

q = 322 kJ

w = -329 kJ

so,

dU = 322 - 329 = -7 kJ

as dU is -ve,

The reaction is exothermic or endothermic : exothermic

The temperature of the water bath goes up or down : up

Does the piston move in or out : out

Does heat flow into or out of the gas mixture : out

How much heat flows : -7 kJ

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