Reaction, urgent.

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 1atm.

The cylinder is also submerged in a large insulated water bath.

The temperature of the water bath is monitored, and it is determined from this data that 

301.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 system does 136.kJ of work on the piston during the reaction.

__________________

1. Is the reaction endo- or exo- thermic?
2. Does the temp. of the water bath go up or down?
3. Does the piston move in or out?
4. Does the reaction absorb or release energy?
5. How much energy does the reaction absorb or release? Be sure your answer has the correct number of significant digits.

Answer 1

Hello, Abigail,

1. Is the reaction endo- or exo- thermic? Exothermic. 301. kJ of heat flowed out of the system AND did 136. kJ of heat on the piston.
2. Does the temp. of the water bath go up or down? Up. The release of 301.kJ would have been absorbed by the water and it's temperature would have increased to the level predicted by water's specific heat (it's temperature response to energy inflow).
3. Does the piston move in or out? The piston moved out, based on two observations. First, the temperature of the system is increasing, so the gas pressure would also increase. Second, "the system did 136. kJ of work on the piston," which mean energy went into making the piston move.
4. Does the reaction absorb or release energy? Releases energy, since 301. kJ of energy flowed out. That energy was released by the reaction, and should be written as -301. kJ.
5. How much energy does the reaction absorb or release? Be sure your answer has the correct number of significant digits. We are not told what the nature of the 301. kJ energy is, but will assume it is separate from the energy exerted on the piston. So add the two to get the total energy released. 301 + 136 = 437 kJ. I see a decimal point, but no numbers (even zeros) after it. I'm not sure why it is there, so while I'll ignore it in counting sig figs (3), but I'll include it in the answer:
6. 437. kJ

I hope this helps,

Bob