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Lab 1
Heat and Temperature
OBJECTIVES
1. Observe phase transitions and the difference between heat of transformation and
specific heat.
2. Predict and measure the latent heat of fusion and vaporization.
EQUIPMENT
Buckets of hot water and ice water, liquid nitrogen, Styrofoam cups, digital scale, DC
power supply and power resistor, Capstone and temperature probe
THEORY
When heat is added to a substance, its temperature normally rises. This heat absorbed
by an object is called the specific heat and is directly related to the object’s temperature
change T. However, when a substance undergoes a change of phase, e.g., solid to
liquid or liquid to gas, the heat energy goes into doing work against the intermolecular
forces and is not reflected in a change in the temperature of the substance. This heat
energy is called the latent heat of fusion Lf and the latent heat of vaporization LV for
the phase changes that occur at the melting point temperature and boiling point
temperature, respectively.
PROCEDURE
Part 1: Melting Ice and the Latent Heat of Fusion
a. Put a known mass mwater (use about 100−150 grams) of warm water in an insulated
container and measure the temperature of the warm water. If you start with water
about 5 oC to 10oC above room temperature and end with the water about 5 oC to
10oC below room temperature, the heat that sneaks into the cooler room from the
warm water will nearly cancel the heat that sneaks into the cooler water from the
warm room. This improves your results.
b. Add about 5 pieces (about the size of the end of your thumb) of carefully “dried ice”
(dry them with a paper towel) of known mass mice. Stir to keep the system in thermal
equilibrium. Measure the temperature T of the mixture using a temperature probe.
c. Once the mixture reaches a constant final temperature, compute the experimental
heat of fusion Lf,thy from conservation of energy:
 Qwater 
 Qice
heat lost by the water
heat gain by the ice
mwater c water Twater  miceL f,exp  micec water Tice water
d. Write your group result on the whiteboard and determine a class average (Lf,avg) and
a two-standard error confidence interval (2σL). Is the accepted value, Lf, accepted =
333×103J/kg, consistent or inconsistent with the class’s confidence interval? Draw a
distribution curve that clearly shows whether the accepted value falling within or
outside the confidence interval.
e. Questions: (i) What were the most important sources of error in the experimental
procedures? (ii) If the temperature of the ice added to the calorimeter were less than
0oC, how would this affect the results? (iii) Is energy conserved in the phase
transition between water and ice?
1.1
Part 2: Boiling Liquid Nitrogen and the Latent Heat of Vaporization.
a. Connect the power resistor R (=2) to a DC power supply, adjust the voltage to
Vsupply = 9V, and turn off the power supply. With the help of the instructor, setup it up
to measure the voltage V and current I through the resistor.
b. Setup a data table in Excel for measuring the mass of the liquid nitrogen (LN2) for 8
minutes every 15 seconds.
c. Turn off the autoshutdown feature on a digital scale (so it runs continuously) and
nest two Styrofoam cups (prevents ice buildup), then place the nested cups on the
scale, add some LN2, and immerse the resistor. Once the resistor and the LN2 are in
thermal equilibrium, start recording the cup's mass once every 15 seconds using a
stop watch. You will note that it drops steadily as the nitrogen boils off due to the
heat gain from the room.
d. After three minutes, turn on the power supply for two minutes and record the cups
mass once every 15 seconds.
e. Turn the power supply back off and record the cup's mass once every 15 seconds
for an additional 3 minutes.
f. Plot your mass-time data and draw straight lines through the data taken during the (i)
first three minutes and the data taken during the (ii) last three minutes. Determine the
mass of the LN2 (mLN2) boiled off by the resistor from the vertical distance between
the two lines near the center of the heating period. Hint: plot 3 different plots for each
mass interval in Excel and use a Trendline to get the equations for the mass boiled
off by the room.
g. Determine the latent heat of vaporization Lv,thy of the LN2 by assuming that the
electrical energy supplied to the heater Qresistor (equals the thermal energy gained by
the nitrogen as it boiled:
Qresistor  Power  time  voltage  current  time  mLN2L v,thy
h. Write your group result on the whiteboard and determine a class average (Lv,avg) and
a two-standard error confidence interval (2σL). Is the accepted value, Lv,accepted =
1.98  105J/kg, consistent or inconsistent with the class’s confidence interval? Draw
a distribution curve that clearly shows whether the accepted value falling within or
outside the confidence interval.
1.2