The amount of heat provided to a system at constant pressure (qp) is equal to _.
Correct answer: B. Change in enthalpy (ΔH)
- A. Change in internal energy (ΔU)
- B. Change in enthalpy (ΔH)
- C. Change in free energy (ΔG)
- D. Change in temperature only (ΔT)
- E. Change in pressure only (ΔP)
Explanation
At constant pressure, the heat added to a system is equal to the change in enthalpy (ΔH). This is because enthalpy is defined as the sum of the internal energy and the product of pressure and volume (H = U + PV). Therefore, when heat is added at constant pressure, it primarily changes the enthalpy. Option B is correct. Option A is incorrect because internal energy change (ΔU) does not account for the work done by the system, while Option C (ΔG) involves entropy and is related to the spontaneity of reactions, not just heat change. Options D and E are unrelated to the direct measure of heat at constant pressure.
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About First Law of Thermodynamics
The first law relates heat supplied, work done and the change in internal energy through energy conservation. Problems use sign conventions and apply the law to isothermal, adiabatic, isobaric and isochoric processes. Internal energy is a state function, while heat and work depend on the path followed.
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