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The law of conversation of heat energy

Objective: To mix hot and cold liquid together and predict the temperature of the mixture.

Equipment/Materials: Styrofoam cup, mass scale,

Procedures:
1. Take a dry Styrofoam cup mass the cup and record.
2. Pour about 50 mL to 60 mL cold water in the cup. Mass the cup + cold H2 O. Record.
3. Take the temperature of cold H2 O and record.
4. Take about 90 mL to 100 mL of hot water.
5. Record the temperature of hot H2 O.
6. Mix the hot water with cold water. Stir gently and take the temp of the mixture.
7. Record the mass of the cup + cold H2 O+ hot H2 O.
8. Clean up work area.


Data:
Mass of Styrofoam = 3.9g
Temperature of cold water = 21̊C
Mass of Styrofoam cup + cold water = 52.9g
Temperature of hot water = 72̊C
Mass of Styrofoam cup + cold water + hot water = 142.1g
Temperature of the mixture = 51̊C

Calculations:
1. Calculate the mass of cold water.
Mass of cup + cold water –mass of Styrofoam

52.9g – 3.9g = 3.0g

2. Calculate the mass of hot water.

Mass of Styrofoam cup + cold water + hot water - Mass of cup + cold water

142.1g – 52.9.9g = 89.2g








3. Calculate the temperature of the mixture by applying the law of converstion of heat and energy:

(m ∆T Cp)cold water =(m ∆T Cp)hot water


(49.0g)(x-21)̊C (4.184 J/g ̊C) = 89.2g (72-x)̊C (4.184 J/g ̊C)

49.0x – 1029 = -89.2x + 6422.4
+89.2x +89.2x
138.2x – 1029 = 0 + 6422.4
+ 1029 +1029__
0 7451.4

138.2x= 7451.4
138.2...