Phys 142
Allan Hancock College
Thermodynamics: Mixing Hot and Cold
PURPOSE
The purpose of this activity is to use the Temperature Sensor to record the temperature of cold
and hot liquids before and after they are mixed.
THEORY
Temperature is a measure of the average kinetic energy (energy of motion) of the particles in a
substance. The thermal energy in the substance depends on three factors:
 amount of the substance (mass)
 specific heat capacity of the substance
 temperature of the substance
The movement of thermal energy from a substance is called heat. The heat that moves from (or
to) a substance depends on the mass of the substance, the specific heat capacity of the substance,
and the change in temperature of the substance. When substances of different temperatures are
mixed, heat moves from one to the other until the temperature of the mixture reaches a balance
called equilibrium.
PROCEDURE
For this activity, the Temperature Sensor measures the temperature of a hot liquid and the
temperature of a cold liquid before they are combined. The Temperature Sensor then measures
the temperature of the combined liquids.
This activity has three parts. The first part, the amount of hot liquid is the same as the amount of
cold liquid. In part two and three, you will use different amounts of each liquid. You will make
predictions for the final equilibrium temperature for the mixture based on the temperature of the
hot and cold liquids before they are mixed.
Computer Setup
1. Connect the Science Workshop interface to the computer, turn on the
interface, and then turn on the computer.
2. Connect the Temperature Sensor DIN plug into an Analog Channel on
the Science Workshop interface.
3. Open a Graph display of temperature versus time.
 Under Sampling Options, set: Periodic Samples = Fast at 10 Hz.
PART 1.
 Put 100 ml (milliliters) of cold water into the first container so that it is slightly less than half
full.
 Put 100 ml of hot water into the second container so that is also slightly less than half full.
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Place the Temperature Sensor into the cold water. Click the REC button to begin recording
data. Watch the values of temperature in the Graph display.
After about 40 seconds, move the Temperature Sensor to the hot water.
After a total of 80 seconds, remove the Temperature Sensor from the hot water. Pour the hot
water into the cold water.
Quickly place the Temperature Sensor into the combined liquids. Stir to thoroughly mix the
two liquids.
Click the STOP button to end data recording after 200 seconds.
PART 2.
 Repeat steps for part 1, except use 50 ml of hot water and 100 ml of cold water.
PART 3.
 Repeat steps for part 1, except use 100 ml of hot water and 50 ml of cold water.
DATA TABLE
Mixing Ratio
Starting temp.
of Hot water
Starting temp.
of Cold water
Predicted temp
of mixture
Actual temp. of
micture
100 ml hot/
100 ml cold
50 ml hot/
100 ml cold
100 ml hot/
50 ml cold
QUESTIONS
1. How do the final temperatures compare to your predictions?
2. Write a sentence that describes how to predict a final temperature for a mixture of hot and
cold liquids based on the amount of each liquid and the starting temperature of each liquid.