Internal energy, ΔE:
For heat, q:
▪ + q → if the system gains, takes in, or absorbs heat or energy
▪ – q → if the system loses, evolves, gives off, or releases heat or energy
For work, w:
▪ + w → work is done on the system by the surroundings (volume: compresses)
▪ – w → work is done by the system on the surroundings (volume: expands)
You may want to reference (Pages 166 - 172)Section 5.2 while completing this problem.
A mixture of gases A2 and B2 are introduced to a slender metal cylinder that has one end closed and the other fitted with a piston that makes a gas-tight seal so that the gases are a closed system. The cylinder is submerged in a large beaker of water whose temperature is 25˚C, and a spark is used to trigger a reaction in the cylinder. At the completion of the reaction, the piston has moved downward, and the temperature of the water bath has increased to 28˚C. If we define the system as the gases
inside the cylinder, which of the following best describes the
signs of q, w, and ΔE for this reaction?
(a) q < 0, w < 0, ΔE < 0
(b) q < 0, w > 0, ΔE < 0
(c) q < 0, w > 0, the sign of ΔE cannot be determined from the information given
(d) q > 0, w > 0, ΔE > 0
(e) q > 0, w < 0, the sign of ΔE cannot be determined from the information given
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