Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
1/6 1 2 7 July 2008 3 July 2008
COURSE DESCRIPTION COURSE TITLE: THERMODYNAMICS LABORATORY TOPIC: BOYLE’S LAW
1 .0
OBJECTIVE To determine the relation between pressure and volume at a given constant temperature
2 .0
EQUIPMENT Gas thermometer, hand vacuum and pressure pump, stand base, stand rod and 2 units of clamp with jaw clamp
3 .0
INTRODUCTION Gases behave differently from the other two commonly studied states of matter, solids
and liquids, so we have different methods for treating and understanding how gases behave under certain conditions. Gases, unlike solids and liquids, have neither fixed volume nor shape. They are molded entirely by the container in which they are held. The gas laws are physical laws describing the behavior of a gas under various conditions of pressure, volume, and temperature.One of the earlier gas laws is Boyle’s law (advanced by Robert Boyle in 1662). He investigated the relationship between the volume of a dry ideal gas and its pressure.
Prepared by: Panel of Thermo-Fluid
Approved by: Head of Plant & Automotive Engineering Department
Signature:
Signature:
Name: Penyelaras Makmal Termodinamik
Name: Dr. Ahmad Jais bin Alimin
Date:
Date:
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
2/6 1 2 7 July 2008 3 July 2008
Since there are four variables that can be altered in a gas sample, in order to investigate how one variable will affect another, all other variables must be held constant or fixed. Boyle fixed the amount of gas and its temperature during his investigation. He found that the pressure and volume of a gas are inversely proportional to one another, or pV = k, where p is pressure, V is volume, and k is a constant of proportionality. A practical math expression of Boyle’s finding is as follows p1V1 = p2V2 where,
4.0
1
= initial value
2
= final values
THEORY In this experiment, the Boyle’s law is confirmed by means of a gas thermometer. The gas
thermometer consists of a glass capillary open at one end. A certain quantity of air is enclosed by means of a mercury seals. At an outside pressure, po, the enclosed air has a volume, Vo. By pumping off air at room temperature with a hand pump, an under pressure ∆p with respect to the outside pressure is generated at the open end of the capillary. The mercury seal itself exerts a pressure on the enclosed air. pHg = ρ Hg .g. hHg where, ρ Hg
= density of mercury
= 13600 kg/m3 ;
g
= acceleration of gravity = 9.82 m/s2 ; and
hHg
= height of the mercury seal (m)
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
3/6 1 2 7 July 2008 3 July 2008
Therefore, the pressure of the enclosed air is, p = p0 + pHg + ∆p where, p0
(bar)
= atmosphere pressure
pHg
= pressure of mercury
∆p
= pressure differential
The volume, V of an enclosed air column is determined by the pressure, p. V can be calculated from the height, h of the air column and the cross-section of the capillary , where, V = A.h =
d 2 .h 4
(m3)
and d = inner diameter of the capillary = 2.7 mm 5.0 EXPERIMENTAL PROCEDURES a. Mount the gas thermometer in the stand device and ensure there is no mercury spilled. b. Ensure the reading of hand pump is 0 mbar, or push the ventilation valve of the hand pump to reduce the pressure differential, ∆p to 0. c. Measure and record the ambient temperature , To and the atmosphere pressure, po. d. Measure the height of the mercury seal, hHg from the scale of the gas thermometer. e. Read and record the height of the air column, h at ∆p = 0 (before apply the pressure differential). f. Generate the pressure differential, ∆p = -50 mbar, read the height of the air column, h and record it together with ∆p. g. Repeat step (f) and record the data for every increment of -50 mbar until it reaches the maximum value of h. h. Measure the reading of ambient temperature, To and atmospheric pressure, po again. (Note: Do not increase or decrease the pressure differential, ∆p too quickly. This can cause the mercury to overshoot and cause a spill)
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
4/6 1 2 7 July 2008 3 July 2008
6.0 EXPERIMENT RESULTS AND DISCUSSION
a.
Complete the Table 1: Pressure and Volume measurements.
b.
Plot pressure, p (bar) against volume, V (m3).
c.
Plot 1/p (bar) against volume, V (m3). Determine the slope of the graph which represents the value of constant C.
d.
Discuss the observation during the experiment and both of the graphs plotted.
e.
Discuss whether Boyle’s Law is true for the sample of gas used in this experiment (air). If yes, calculate the final value of pV and compare with the value of constant C obtained from the plot 1/p against V. Discuss about the error and the factors that will affect the result of this experiment.
7.0 QUESTIONS
a. Why the ambient temperature needs to be measured before and after the experiment? b. What is the effect if the mercury in the gas thermometer spilled? c. For a given fixed quantity of gas, the deviations of the ’ideal’ behaviour of Boyle’s Law will be smallest at large or small volume? Give the justification of your answer.
8.0 CONCLUSION
Give conclusions from the experiment.
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
Hand pump
5/6 1 2 7 July 2008 3 July 2008
Mercury seal
h (height of air column)
Ventilation valve
Figure 1: Boyle’s Law Apparatus
Document Reference No. Document Title
RPP-05
Page No.
LABORATORY EXPERIMENT
Edition Revision No. Effective Date Amendment Date
6/6 1 2 7 July 2008 3 July 2008
Data sheet: Atmosphere pressure, po (bar) = _______ (before experiment) _______ (after experiment) Ambient temperature, To (oC) = ______ (before experiment) ______ (after experiment) Height of mercury seal, hHg
= ________ (mm)
Table 1: Pressure and Volume Measurements ∆p (mbar)
h (mm)
p (bar)
1/p (bar)
V (m3)
