Mug Of Coffee/thermodynamics

[Answerprancer]

Does anyone know the answer to this:
Some time ago, I was involved in a discussion re heating up mugs before dispensing coffee or tea into them, the question being - will this slow down the natural cooling of the liquid or actually speed it up?

[woofgang]

I think slow it down. My reasoning is that entropy seeks to smear out differences. The coffee will have to pass less heat to the mug to make is the same temperature as the adjacent coffee so it will retain more heat itself.

[woofgang]

but....I guess it will depend on what the mug is made of. If the mug is a good conductor, say metal, then it would quickly shed its own heat and start to draw hat from the coffee.

[murraymints]

depends on which is hottest I suppose...

[woofgang]

oh yeah. I assumed that the coffee was hotter than the mug

[Old_Geezer]

I'd need some convincing that adding energy would encourage a greater rate of energy loss. Surely the liquid will cool down more slowly ?

[wildwood]

It must slow down the cooling as the mug will draw less heat from the coffee.

[Fitzer]

I remember doing this in physics 35 years ago, if you pour a hot liquid into a cold vessel the temperature of the combined liquid/cup will reduce by a given amount depending upon the temperature coefficient of the vessel. Therefore heating the vessel will reduce the amount the liquid cools by. Type of material and weight of vessel will have a significant effect on the cooling. This is why espresso machines in coffee shops have the cups on top so that they are kept warm to prevent the coffee cooling too much when it is poured.

[Graham-W]

Another interesting conundrum is the "hot water freezes more quickly than cold water" puzzle.
Solve it and earn yourself a grand: http://www.dailymail.co.uk/sciencetech/article-2165277/Scientists-offer-1-000-prize-answer-question-Why-does-hot-water-freeze-faster-cold.html

[Answerprancer]

Great responses so far. Thanks.
I was thinking that if the mug was pre-warmed then the cooling of the added hot liquid would depend on the material that the container was made of as Woofgang suggested.
I wonder then what would happen to a mug of hot coffee that was contained within a pre-warmed stainless steel mug compared to a similarly hot drink dispensed into a cold stainless steel mug, additionally, I wonder what effect the ambient temperature would have on the speed of cooling.

[wildwood]

It is the same thing.... a pre-warmed stainless steel mug will draw less heat from the drink so takes longer to cool.

The ambient temperature always has some bearing on the cooling, however small. Hot coffee in a warm SS mug in a cold room will cool faster than in a warm room. The mug acts as a sort of conducter between the liquid and the room. One of those thermo mugs will minimise the heat transfer so keeps the liquid warm longer.

[Peter Pedant]

Pitzer I thought gave a good answer

This is a straightforward q on heat content ( em ess theta and all that) and cooling (Newton's 5/4ths law and all that)

Since you arent making your cuppa coughee work,
it isnt thermodyamics wh however is a cute word to use in a headline

Since youa re heating the cup, you are increasing the total heat in the system and so it will take longer to cool.

I love the hot plate analogy and wish I thought of it myself (I love it so much)

I think we all assume that something at 37'C or whatever will have the same cooling characteristics no matter how you arrived at that final temperature.

IN the hot and cold water red herring, that clearly doesnt apply.

[Zacs-Master]

Isn't ambient temperature a factor?

[jomifl]

Yes, but it is assumed to be the same for both cases

[issy]

One cannot get away from the law that work produces heat - in other words nothing is cooled. Cooling only takes place when heat is used up so pouring hot liquid into a hot vessel means that less heat is used up by the hotter item in working to equalise the temperature of the two bodies QED.

[woofgang]

Yup
Flanders and Swann said it best Media URL: http://m.youtube.com/watch?v=VtEqn-5XHpU
Description:

[woofgang]

Hmmm