# Thermodynamics: Mixing Hot and Cold

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27 Οκτ 2013 (πριν από 4 χρόνια και 8 μήνες)

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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 ho
t
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)

sp
ecific 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 subst
ance, and the
change i
n 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.
T
he
first part
, the amount of h
ot 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 a
re 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 = F
ast
at

10 Hz
.

PART

1
.

Put 100 ml (milliliters) of cold water into the first cont
ainer 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.

Place the Temperature Sensor into the cold water. Click the
REC

button to begin recor
ding 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 wa
ter.

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
20
0 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
10
0 ml

of hot water and
5
0 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

5
0

ml hot
/

100 ml cold

100

ml hot
/

5
0 ml cold

QUESTIONS

1.

How
do the final temperatures