Hot water increases not only the speed of solubility but also the amount.
I don't know whether this is for all materials in water, apart from salt.
But, if this is the case, what causes hot water to dissolve more salt (or other solutes)?
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1$\begingroup$ Searching for 'salt solubility in different temperatures' in Google yields many results, among them this simple explanation and this table. I believe most basic chemistry books also cover this topic. $\endgroup$– Don_SJan 12, 2017 at 14:30
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$\begingroup$ Your statement is not generally true. For NaCl, there is only a slight increase in solubility, can be much stronger for others, or even reversed. The reason is thermodynamics, of course, but would be nice if someone worked out when exactly what happens. $\endgroup$– KarlJan 13, 2017 at 6:30
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There seems to be two parts to your question. First, not all substances have increased solubility as water temperature rises. Gasses for example have decreased solubility in this case.
As for the second part of the question, increased heat adds energy to the water molecules which makes it easier to overcome the bonds between $\ce{Na}$ and $\ce{Cl}$. According to Wikipedia, the solubility of $\ce{NaCl}$ in nearly freezing water is $35.65 \, \mathrm{g} / 100 \, \mathrm{mL} \, \ce{H2O}$ versus boiling water which is $38.99 \,\mathrm{g} / 100 \, \mathrm{mL}\, \ce{H2O}$. Hope this helped.
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$\begingroup$ Note that it isn't just gases that exhibit decreased solubility with increased temperature, but many solids also. Calcium hydroxide for example has a solubility in water of 1.89 g/L at 0C, 1.73 g/L at 20C and 0.66 g/L at 100C. $\endgroup$– airhuffMar 5, 2017 at 18:55