If q is the heat added to the system, w is the work done by the system and ΔE is the change in internal energy, than according to the first law of thermodynamics:
Correct answer: B. ΔE = q - w
- A. ΔE = q + w
- B. ΔE = q - w
- C. ΔE = q + P ΔV
- D. ΔE = q + ΔH
Explanation
According to the first law of thermodynamics, the change in internal energy (ΔE) of a system is equal to the heat added to the system (q) minus the work done by the system (w). This is expressed as ΔE = q - w. Option B is correct because it accurately reflects this relationship. Option A incorrectly adds both q and w, which misrepresents the convention for work done by the system. Option C introduces pressure-volume work but does not align with the general form of the first law. Option D mistakenly incorporates enthalpy (ΔH), which is not part of the internal energy change equation in this context.
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About Thermochemistry and Energetics of Chemical Reactions
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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