A student is preparing 250 cm3 of coffee at 85 deg cel in a cup . Given:
Mass of 1 cm3 of coffee/milk = 1 g
Specific heat capacity of milk = 4800J/kg del cel
Specific heat capacity of coffee = 4200J/kg deg cel
Specific heat capacity of copper = 370 J/kg del cel
(i) When she add 50cm3 of milk at 5 deg cel to the coffee what is the final temperature of the coffee? My answer: 70.1 del cel
(ii) She then stirs the coffee with a 100g copper teaspoon at 20 deg cel. What is the temperature of the coffee after she stirs the coffee? (you may ignore any thermal energy transfer between the hand and the teaspoon)
Not sure how to do this.
Is it,
Energy gained by copper teaspoon = Energy lost by coffee+ Energy lost by milk
Do I have to take into account the energy lost by milk? And in any case, when you want to find the energy lost by coffee, you have to know its temperature change. So is temperature of 20 deg cel in the question referring to coffee+milk at 20 deg cel or do I use the 70.1 deg cel (ans found in part(i)) earlier on in the question? Cuz i have to know the intial temperature before being able to subtract or add the final temperature to my equation.
(iii) Some people prefer to add sugar before milk. Can you suggest a reason for that? Why don't they do it the other way round?
Quite a lame question but no solid answer from me. Sugar can dissolve faster?
thanks
ii) Yes you have to take into account energy lost by milk
Because the milk is already inside.
You also use the temperature found in part (i) because part (ii) uses the phrase "She then stirs"...
(iii) Some people prefer to add sugar before milk. Can you suggest a reason for that? Why don't they do it the other way round?
Don't worry, it's not lame.
It's just that sugar dissolves easier in warmer water. After adding milk, the coffee is cooler, so not as easy to dissolve the sugar ;)
Solubility is from chemistry... UltimaOnline might want to add more here ;)
Originally posted by eagle:ii) Yes you have to take into account energy lost by milk
Because the milk is already inside.
You also use the temperature found in part (i) because part (ii) uses the phrase "She then stirs"...
Don't worry, it's not lame.
It's just that sugar dissolves easier in warmer water. After adding milk, the coffee is cooler, so not as easy to dissolve the sugar ;)
Solubility is from chemistry... UltimaOnline might want to add more here ;)
So temperatures of both milk and coffee are the same? Since they are in same mixture anyway. And as for the mass of milk and coffee do i use back 50g and 250g respectively?thanks
Originally posted by bonkysleuth:So temperatures of both milk and coffee are the same? Since they are in same mixture anyway. And as for the mass of milk and coffee do i use back 50g and 250g respectively?thanks
if u add both together at stir they have to be same temperature.
chim