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Diffstat (limited to 'source/know/concept/thermodynamic-potential/index.md')
| -rw-r--r-- | source/know/concept/thermodynamic-potential/index.md | 49 |
1 files changed, 25 insertions, 24 deletions
diff --git a/source/know/concept/thermodynamic-potential/index.md b/source/know/concept/thermodynamic-potential/index.md index b15c011..60eee78 100644 --- a/source/know/concept/thermodynamic-potential/index.md +++ b/source/know/concept/thermodynamic-potential/index.md @@ -12,17 +12,17 @@ layout: "concept" whose minima or maxima represent equilibrium states of a system. Such functions are either energies (hence *potential*) or entropies. -Which potential (of many) decides the equilibrium states for a given system? -That depends which variables are assumed to already be in automatic equilibrium. -Such variables are known as the **natural variables** of that potential. -For example, if a system can freely exchange heat with its environment, -and is consequently assumed to be at the same temperature $$T = T_{\mathrm{env}}$$, +Of the many options, which potential decides the equilibrium state for a given system? +It depends on which variables are assumed to be in automatic equilibrium. +Such variables are called the **natural variables** of that potential. +For example, if a system can exchange heat with its environment, +and is consequently at the same temperature $$T = T_{\mathrm{env}}$$, then $$T$$ must be a natural variable. The link from natural variables to potentials is established by [thermodynamic ensembles](/know/category/thermodynamic-ensembles/). -Once enough natural variables have been found, +Once the natural variables have been determined, the appropriate potential can be selected from the list below. All non-natural variables can then be calculated by taking partial derivatives of the potential @@ -48,8 +48,8 @@ $$\begin{aligned} \end{aligned}$$ It is a function of the entropy $$S$$, volume $$V$$, and particle count $$N$$: -these are its natural variables. -An infinitesimal change $$\dd{U}$$ is as follows: +these are its natural variables, +so an infinitesimal change $$\dd{U}$$ is as follows: $$\begin{aligned} \boxed{ @@ -59,7 +59,7 @@ $$\begin{aligned} The non-natural variables are temperature $$T$$, pressure $$P$$, and chemical potential $$\mu$$. -They can be recovered by differentiating $$U$$ +These can be recovered by differentiating $$U$$ with respect to the natural variables $$S$$, $$V$$, and $$N$$: $$\begin{aligned} @@ -92,8 +92,8 @@ $$\begin{aligned} \end{aligned}$$ It is a function of the entropy $$S$$, pressure $$P$$, and particle count $$N$$: -these are its natural variables. -An infinitesimal change $$\dd{H}$$ is as follows: +these are its natural variables, +so an infinitesimal change $$\dd{H}$$ is as follows: $$\begin{aligned} \boxed{ @@ -103,7 +103,7 @@ $$\begin{aligned} The non-natural variables are temperature $$T$$, volume $$V$$, and chemical potential $$\mu$$. -They can be recovered by differentiating $$H$$ +These can be recovered by differentiating $$H$$ with respect to the natural variables $$S$$, $$P$$, and $$N$$: $$\begin{aligned} @@ -132,8 +132,8 @@ $$\begin{aligned} \end{aligned}$$ It depends on the temperature $$T$$, volume $$V$$, and particle count $$N$$: -these are natural variables. -An infinitesimal change $$\dd{H}$$ is as follows: +these are its natural variables, +so an infinitesimal change $$\dd{H}$$ is as follows: $$\begin{aligned} \boxed{ @@ -142,8 +142,8 @@ $$\begin{aligned} \end{aligned}$$ The non-natural variables are -entropy $$S$$, pressure $$P$$, and chemical potential $$\mu$$. -They can be recovered by differentiating $$F$$ +the entropy $$S$$, pressure $$P$$, and chemical potential $$\mu$$. +These can be recovered by differentiating $$F$$ with respect to the natural variables $$T$$, $$V$$, and $$N$$: $$\begin{aligned} @@ -171,8 +171,8 @@ $$\begin{aligned} \end{aligned}$$ It depends on the temperature $$T$$, pressure $$P$$, and particle count $$N$$: -they are natural variables. -An infinitesimal change $$\dd{G}$$ is as follows: +they are its natural variables, +so an infinitesimal change $$\dd{G}$$ is as follows: $$\begin{aligned} \boxed{ @@ -181,7 +181,7 @@ $$\begin{aligned} \end{aligned}$$ The non-natural variables are -entropy $$S$$, volume $$V$$, and chemical potential $$\mu$$. +the entropy $$S$$, volume $$V$$, and chemical potential $$\mu$$. These can be recovered by differentiating $$G$$ with respect to the natural variables $$T$$, $$P$$, and $$N$$: @@ -210,8 +210,8 @@ $$\begin{aligned} \end{aligned}$$ It depends on temperature $$T$$, volume $$V$$, and chemical potential $$\mu$$: -these are natural variables. -An infinitesimal change $$\dd{\Omega}$$ is as follows: +these are its natural variables, +so an infinitesimal change $$\dd{\Omega}$$ is as follows: $$\begin{aligned} \boxed{ @@ -239,7 +239,8 @@ $$\begin{aligned} ## Entropy The **entropy** $$S$$, in units of energy over temperature, -is an odd duck, but nevertheless used as a thermodynamic potential. +is an odd duck, but nevertheless used as a thermodynamic potential, +to be maximized instead of minimized. It is given by: $$\begin{aligned} @@ -249,8 +250,8 @@ $$\begin{aligned} \end{aligned}$$ It depends on the internal energy $$U$$, volume $$V$$, and particle count $$N$$: -they are natural variables. -An infinitesimal change $$\dd{S}$$ is as follows: +they are its natural variables, +so an infinitesimal change $$\dd{S}$$ is as follows: $$\begin{aligned} \boxed{ |
