zenterix
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- Homework Statement
- Consider the proton transfer reaction between water molecules
- Relevant Equations
- $$\mathrm{H_2O(l)+H_2O(l)\leftrightharpoons H_3O^+(aq)+OH^-(aq)}$$
The equilibrium constant is
$$K=\frac{a_{\mathrm{H_3O^+}}a_{\mathrm{OH^-}}}{(a_{\mathrm{H_2O}})^2}$$
where ##a_J## denotes the activity of a solute ##\text{J}## in a dilute solution, ##\mathrm{[J]}/c^\circ## with ##c^\circ=1\mathrm{mol\cdot L^{-1}}##.
The book I am following says that the solvent, water, is very nearly pure, "and so its activity may be taken to be 1".
Where does this 1 come from?
It certainly is not $$\mathrm{[H_2O]/c^\circ}$$.
$$K=\frac{a_{\mathrm{H_3O^+}}a_{\mathrm{OH^-}}}{(a_{\mathrm{H_2O}})^2}$$
where ##a_J## denotes the activity of a solute ##\text{J}## in a dilute solution, ##\mathrm{[J]}/c^\circ## with ##c^\circ=1\mathrm{mol\cdot L^{-1}}##.
The book I am following says that the solvent, water, is very nearly pure, "and so its activity may be taken to be 1".
Where does this 1 come from?
It certainly is not $$\mathrm{[H_2O]/c^\circ}$$.