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CHEM254 Chapter Notes -Ideal Gas, Exact Differential, Intensive And Extensive Properties

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William Power

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- The reversible work is the lower bound for the compression work and the upper bound for the
expansion work
- The maximum work that can be extracted from a process between the same initial and final
states is that obtained under reversible conditions
- What does the first law look like under reversible and constant pressure conditions?
o We write: look on page 30 for eq’n
o H = U + PV
- Because chemical reactions are much more frequently carried out at constant P than constant V,
the energy change measured experimentally by monitoring the heat flow is deltaH rather than
- Because U is a state function, deltaU is independent of the path between the initial and final
- If one knows Cv, T1, and T2, deltaU can be calculated, regardless of the path between the initial
and final states
- Eq’n 2.34
- Because deltaH is a function of T only for an ideal gas, this eq’n holds for all processes involving
ideal gases, whether P is constant or not as long as it is reasonable to assume that Cp is constant
- If the initial and final temperatures are known or can be calculated, and if Cv and Cp are known,
deltaU and deltaH can be calculated regardless of the path for processes involving ideal gases,
as long as no phase changes occur
- The first law links q, w, and deltaU
- If any two of these quantities are known, the first law can be used to calculate the third
- The integral that needs to be evaluated: 2.35
- 2.36
- Because Pexternal is not equal to P, the work considered in the equation above is for an
irreversible process
- Reversible: 2.37
- deltaU = deltaH = 0 for an isothermal process because deltaU and deltaH depend only on T
- for an adiabatic process, q = 0, deltaU = w
- if only expansion work is possible, w = 0 for a constant volume process
- reversible adiabatic compression of a gas leads to heating, and reversible adiabatic expansion
leads to cooling
chapter 3
- eqn 3.2
- eqn 3.5
- exact differential: when f can be expressed as an infinitesimal quantity, df, that when integrated
depends only on the initial and final states
- an example of a state function and its exact differential is U and dU = dq Pext*dV
- B = isobaric volumetric thermal expansion coefficient
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