A gas reaction is allowed to take place in a canister while submerged in water at a temperature of 25^oC. The gas expands and does P-V work on the surroundings equal to 385 J. At the same time, the temperature of the water decreases to 20^oC as the energy in the gas reaction reaches 364 J. What is the change in energy of the system? 

• A. 21 J
• B. -32 J
• C. -21 J
• D. 134 J

Answer: (C)

Verified step by step guidance

1. Identify the components of the system and surroundings. The system is the gas undergoing the reaction, and the surroundings include the water and the canister.
2. Understand the concept of energy change in a system. The change in energy (ΔE) of a system is given by the formula: ΔE = q + w, where q is the heat exchanged and w is the work done.
3. Determine the values given in the problem. The work done by the system (P-V work) is 385 J, and the energy from the gas reaction is 364 J. The temperature change in the water indicates heat exchange.
4. Calculate the heat exchanged (q). Since the temperature of the water decreases, the system loses heat. The energy from the gas reaction is 364 J, which is the heat lost by the system.
5. Apply the formula for energy change: ΔE = q + w. Substitute q = -364 J (since heat is lost) and w = 385 J (work done by the system) into the formula to find the change in energy of the system.