1) If 100.0mL water of at 50.0C is added to 100.0 mL of water at 20.0C. What tem
ID: 916344 • Letter: 1
Question
1) If 100.0mL water of at 50.0C is added to 100.0 mL of water at 20.0C. What temperature would the mixture of water reach? Assume the system is perfectly sealed and no heat is lost to the calorimeter or to the outside environment.
2) If a student’s coffee cups are discarded after the first HCl reaction and new coffee cups are used only for the final reaction with acetic acid. Which calculated values will be affected by this error?
3) A chemistry professor has a cup of coffee containing 50.0mL of room temperature coffee at 25.0C. The professor also has a new pot of hot coffee at temperature of 96.0C. What volume of hot coffee will the professor need to add to his cold coffee to reach the ideal drinking temperature of 82.0C? Assume that no heat is lost to the coffee cup or to the environment. Also assume that coffee has the same density (1.0g/mL) and heat capacity (4.184 J/g*C) as water.
Explanation / Answer
1) Heat lost = Heat gained
q(hot water) = q(cold water)
mCpdT(hot) = mCpdT(cold
let Tf be the final temperature
density of water = 1 g/ml, so volume = mass
100 x 4.184 x (50 - Tf) = 100 x 4.184 x (Tf - 20)
20920 - 418.4Tf = 418.4Tf - 8368
29288 = 836.8Tf
Tf = 35 oC is the final temperature
2) If the student discards the coffee cup after the first HCl reaction, the change in temperature measured and thus the final heat of reaction would be lower than the actual value and results would be incorrect.
3) Heat lost = Heat gained
mCpdT(hot) = mCpdT(cold)
m x 4.184 x (96 - 80) = 50 x 4.184 x (80 - 25)
m = 171.87 g
density of water = 1 g/ml
The professor need to add 171.87 ml of hot coffee.
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