Multiple Choice
Which type of reaction releases energy to the surroundings?
8. Thermochemistry
Endothermic & Exothermic Reactions
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If a cylinder equipped with a piston expands against an external pressure of 1.25 atm, increasing the volume of a cylinder by 0.500 L and releasing 25.0 J of heat, what is ΔE for the process?
A
−88.3 J
B
−63.3 J
C
63.3 J
D
0.625 J
E
−25.6 J
Verified step by step guidance1
Understand the problem: We need to find the change in internal energy (ΔE) for a process where a cylinder expands against an external pressure, increases in volume, and releases heat.
Recall the formula for change in internal energy: ΔE = q + w, where q is the heat exchanged and w is the work done.
Identify the values given: q = -25.0 J (since heat is released, it's negative), external pressure = 1.25 atm, and change in volume (ΔV) = 0.500 L.
Convert the pressure-volume work from atm-L to Joules using the conversion factor: 1 L atm = 101.3 J. The work done by the system is w = -PΔV, where P is the external pressure.
Calculate the work done: w = -(1.25 atm) * (0.500 L) * (101.3 J/L atm). Substitute this value into the formula for ΔE: ΔE = q + w.
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