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I usually make tea by adding two spoons of tea powder to water at room temp. and start to heat it. My friend said it will be better to add the powder once the water starts boiling. She said that it will dissolve tea more easily because of the sudden temperature difference experienced by tea powder.

Does it make a difference? Why?

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I would say that your method is actually quicker (if that's what you mean by 'better'). My reasoning is as follows: the solubility of the powder in water increases with increasing temperature, as does the dissolution rate but the dissolution rate remains finite all the time.

1) If you add the powder and start heating at $t=0$ the concentration of dissolved powder will start to increase from $c=0$ to $c>0$ immediately. Once the water reaches the boiling point at $t=t_b$ already a certain amount (maybe even all) of the powder has dissolved i.e. some concentration of dissolved powder is present $c=c_1$.

2) If you boil the water first and then add the powder you start with $c=0$ at $t=t_b$, which is a lower concentration than in the powder-first case.

Because there is already more powder dissolved at the boiling point ($c=c_1$ vs. $c=0$ at $t=t_b$), the moment at which all powder is dissolved comes sooner for the powder-first case (situation 1).

Note that I approach this question purely from the physical point of view, I have no clue whether the two methods might result in differently tasting tea.

P.S. I ignored any possible changes in the boiling point due to the already dissolved powder. For low concentrations, as in the case of tea, this is no problem. If the concentrations become much higher then the change in boiling point might become dominant and the story changes

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  • $\begingroup$ Essentially if put your tea in the room temperature water, the total time to dissolve will be longer, but the time to dissolve from the beginning of boiling would be shorter if you add your tea to room temperature water. $\endgroup$ – A.K. Dec 13 '15 at 15:25
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Your friend is right. As the temprature increases, the solubility of tea increases. Hence your tea will dissolve more easily when the water is heated before adding the tea powder, rather than your method.

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    $\begingroup$ This doesn't explain why heating first then adding powder would be better then adding powder then heating. The solubility/temperature effect is there in both situations. Could you clarify why the heating then powder would be better?! $\endgroup$ – Michiel Feb 21 '14 at 17:56

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