Question

= OTHERMOCHEMISTRY 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 245. KJ of energy. The temperature of the water bath is monitored, and it is determined from this data that 264. KJ of heat flows out of the system during the reaction. Is the reaction exothermic or endothermic? exothermic endothermic x 5 ? down Does the temperature of the water bath go up or down? neither out Does the piston move in or out? does work work is done on it Does the gas mixture do work, or is work done on it? neither (Explanation Check

Answer 1

In this examp flows our this example 264 KJ of heat - the system during the reaction. If energy leaves the system, its sign is negative q = -264 KJ. khen energy / heat flows out, it is exothormic reaction & in case of exothermic reaction piston moves up lathen piston moves up work is I done by the system on the surrounding takes If work is done by the system, its sign i let = -ve (for exothermic reacHon) hplace is negative Reaction is exothermic. . Temperature of water bath go up ie increases because water absorb the heat which is given out by system. piston moves up le. out because this is exothermic reaction & during this reaction piston moves up ie, our Here gas mixture do work. . According to first law Of Thormodynamics du= dq - dk Here duro dq = - 264 KI (Work done is negative) 0 - - 264 KJ - (W) - Kat 26K KJ