How Do You Calculate the Amount of Heat Transferred in Thermodynamics?

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SUMMARY

The discussion focuses on calculating the amount of heat transferred in thermodynamics using the enthalpy change equation. The key equation presented is h_2 - h_1 = (u_2 + P_2v_2) - (u_1 + P_1v_1), which relates changes in internal energy and pressure-volume work. The user identifies that when pressure is not listed, one should refer to saturated liquid tables at the given temperature to find the enthalpy values. The conclusion drawn is that if there is no change in enthalpy between constant temperatures, the overall enthalpy change is zero.

PREREQUISITES
  • Understanding of thermodynamic concepts such as enthalpy and internal energy.
  • Familiarity with saturated liquid and compressed liquid tables.
  • Knowledge of the equation ΔH = ΔU + Δ(PV) and its components.
  • Basic grasp of pressure-volume work in thermodynamic processes.
NEXT STEPS
  • Study the use of saturated liquid tables in thermodynamic calculations.
  • Learn how to apply the equation ΔH = ΔU + VΔP in various scenarios.
  • Explore the implications of constant temperature processes on enthalpy changes.
  • Investigate the significance of internal energy changes in thermodynamic systems.
USEFUL FOR

Students studying thermodynamics, engineers working with heat transfer calculations, and professionals involved in energy systems analysis will benefit from this discussion.

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Homework Statement



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Homework Equations



h_2 - h_1 = (u_2 + P_2v_2) - (u_1 + P_1v_1)

The Attempt at a Solution



I thought I had to look at the charts in the book for saturated liquid, then notice that the temperature is much higher at the given pressure than what was given in the problem. That would tell me for both situations I have a compressed liquid. But the thing is when our pressure isn't listed in the compressed liquid tables, we are supposed to look at the saturated liquid tables under the given temperature to determine an equivalent amount for what we are trying to solve. In this case it would be enthalpy. And this is true for both cases, which would make the enthalpy zero overall as there is no change in enthalpy between constant temperatures. So I must be approaching this wrong. What is another method to solve this problem?
 
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ΔH = ΔU + Δ(PV) = ΔU + VΔP + PΔV

Since ΔV = 0 (it is negligible) this is simply: ΔH = ΔU + VΔP

What is ΔU here? What is VΔP?

AM
 

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