Mixture and conservation of en

用戶190687

2009-11-15 6:50 am

2.Some milk at 25C is added to a cup of hot tea of 250g at 95C.The specific heat
capacities of the milk and the tea are 4000J kg^-1 C^-1 and 3800J kg^-1 C ^-1
respectively.
a)If the final temperature of the milk has been added?Assume there is no heat
lost to the surroundings.
b)Instead of milk,two identical slices of lemon,each of a heat capacity of 40J C^-1 and temperature of 30C,are added to the tea.Calculate the total energy transferred from the tea to the two slices of lemon.

回答 (1)

天同

2009-11-16 6:28 am

✔ 最佳答案

(a) You seem to have missed out typing some information in the question. The sentence reads odd !!!
I believe the question has given the final temperature of the milk-tea mixture, and asked for the mass of milk added. If that is the case,

Let T be the GIVEN final temperature of the milk and tea
Heat absorbed by milk = m.(4000).(T-25)
where m is the mass of milk added
Heat given out by tea = (250/1000).(3800).(95-T)
using the heat balance equation,
m.(4000).(T-25) = (250/1000).(3800).(95-T)
i.e. m = [(250/1000).(3800).(95-T)]/[.(4000).(T-25)]

(b) The heat balance equation now becomes:
2 x 40 x (T'-30) = (250/1000).(3800).(95-T')
where T' is the final temperature of the mixture

After solving for T', the total energy transferred from the tea to the two lemon pieces is given by the term (250/1000).(3800).(95-T') J

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