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Gas Laws Flashcards

1
Q

What is the General Gas Law?

A

PV/T=Constant or P1V1/T1=P2V2/T2

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2
Q

What is the formula to find the final pressure P2?

A

P2=P1V1T2/V2T1

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3
Q

What is the formula to find the final volume V2?

A

V2=P1V1T2/P2T1

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4
Q

What is the formula to find the final temperature T2?

A

T2=P2V2T1/P1V1

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5
Q

What does the General Gas Law show?

A

That if any two properties of a gas are changed the third property will also change

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6
Q

What is an important reminder when using the General Gas Equation?

A

That the temperature must be in Kelvin

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7
Q

What is cubic expansivity of a gas (γ)?

A

Increase in volume per unit volume at 0°C per degree celsius rise in temperature

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8
Q

If V0= Volume at 0°C and Vt= Volume at t°C then what is the formula for cubic expansivity of a gas?

A

γ=(Vt-V0)/(V0 x t)

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9
Q

What is the value of the fraction γ in the equation for cubic expansivity of a gas?

A

1/273

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10
Q

Is the cubic expansivity of a gas the same or different for all gases?

A

The same

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11
Q

How does the cubic expansivity of a gas compare to that of solids and liquids?

A

It is different

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12
Q

What is an important point to note about the cubic expansivity of a gas?

A

That the cubic expansivity of a gas is calculated from the fractional increase of its volume at 0°C

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13
Q

If the graph of fig 10.12 is produced backwards where will it cut the temperature axis?

A

At a temperature of -273°C

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14
Q

What does the graph cutting the temperature axis at -273°C imply?

A

That the volume of a gas is theoretically zero at -273°C if the gas has not liquefied before that temperature

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15
Q

What is the temperature -273°C called?

A

The absolute zero of temperature

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16
Q

What is the absolute zero of temperature considered to be?

A

The lowest possible temperature of a gas

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17
Q

What is a temperature scale in which the value of the degree is the same as the Celsius degree but whose zero point is the absolute zero of temperature or -273°C known as?

A

The thermodynamic or Absolute or Kelvin (K) temperature scale

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18
Q

How is a temperature t°C on the Celsius scale related to an absolute or Kelvin temperature T?

A

T(K)=273+t°C

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19
Q

Using this scale how can Charles’ law be stated?

A

The volume of a fixed mass of gas is directly proportional to its absolute temperature if its pressure remains constant

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20
Q

In symbols how does Charles’ law state this?

A

V/T= Constant if the pressure is kept constant or V1/T1=V2/T2

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21
Q

From what can this new statement of Charles’ law be derived?

A

From the graph of volume of gas against temperature at constant pressure (fig 10.13)

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22
Q

Since V0/273 is a constant what can we state?

A

That V∝T or the volume of a given mass of gas at a constant pressure is proportional to its absolute or Kelvin temperature T

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23
Q

If in our experiment to verify Charles’ law we plot the volume of the gas against its absolute temperature what kind of graph will we obtain?

A

A straight line graph passing through the origin (fig 10.14)

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24
Q

What is Charles’ law?

A

Charles law gives the relationship of the volume of a gas to its temperature at constant pressure

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25
What does Charles' law state?
The volume of a fixed mass of gas increases by 1/273 of its volume at 0°C per degree Celsius rise in temperature provided its pressure remains constant
26
How can we verify Charles' law in the laboratory?
Using the apparatus shown in fig 10.11
27
Describe the apparatus used to verify Charles' law.
A column of dry air is trapped by a pellet of mercury in a capillary tube of uniform diameter which has been previously cleaned and dried The tube is then sealed at one end It is tied together with a thermometer to a half-metre rule by means of two rubber bands and placed inside a beaker of water with enough water to cover most of the capillary tube Some ice shavings are added to the water in the beaker until the temperature of the mixture gets down to about 0°C The exact temperature is read with the thermometer after the water has been continually stirred to ensure an even temperature
28
What is done after the temperature of the mixture gets down to about 0°C?
The length of the air column is now read over the metre scale and recorded against the temperature The water is now heated gently and lengths of the air columns at different temperatures are read as the temperature of the water rises Before each reading of temperature the water should be stirred to obtain an even distribution The results are recorded as shown in table 10.2
29
Because the tube is of uniform cross-section what can we take the volume of the gas as proportional to?
Its length
30
What is then plotted against the corresponding temperature?
A graph of volume (or length) of gas
31
What kind of graph is obtained and what does its slope indicate?
The graph obtained is a straight line whose slope is approximately 1/273
32
Since the volume of gas was under a constant pressure what do we conclude?
That Charles' law has been verified
33
What are the precautions to take when verifying Charles' law?
Temperatures are taken when the thermometer reading is steady Water must be continuously stirred to ensure even temperature The bore of the tube must be clean and dry Only dry air or gas should be used It is essential to carry out the experiment slowly so that heat has time to pass through the thick walls of the capillary tube and bring the gas to the same temperature as the water in the beaker
34
What is the height of water that will support 1 atmosphere of pressure?
10.34 m
35
What is the relationship between the pressure and the volume of a fixed mass of a gas?
Boyle's Law
36
What does Boyle's law state?
The pressure of a fixed mass of a gas is inversely proportional to its volume provided that the temperature is kept constant
37
In symbols how is Boyle's law written?
P∝1/V or PV=constant where P is the pressure and V is the volume of a fixed mass of gas
38
How can we verify Boyle's law in the laboratory?
Using a simple apparatus
39
Describe the simple apparatus used to verify Boyle's law.
Some dry air is enclosed in a glass tube of uniform cross-section attached by rubber tubing to a mercury reservoir By raising or lowering the open tube B the length of the air column in C can be varied This length which can be read against the metre scale is taken as a measure of the volume of the gas since the tube has a uniform cross-section The difference (h) in the levels of mercury at C and B is read for each value of the length of gas The atmospheric pressure (H) is read from a Fortin barometer
40
When the mercury surface in B is lower than that in C what is the pressure of gas given by?
P=(H-h) cm Hg
41
When the mercury surface in B is higher than that in C what is the gas pressure P given by?
P=(H+h) cm Hg
42
What are the precautions to take when verifying Boyle's law?
There should be no air bubbles in the mercury Only dry air should be used in the experiment Readings should be taken when the mercury levels are steady Time must be allowed for the air to assume room temperature the constant temperature for the experiment
43
What is the pressure of the atmosphere at sea level?
76 cm of mercury (or 76 cm Hg)
44
What is 76 cm Hg taken as?
The standard (or normal) pressure
45
Since pressure is defined as force per unit area how can we derive the equivalent of 76 cm Hg in Newtons per square metre the S.I. unit?
We recall that P=hρg h=76 cm Hg=0.76 m Hg ρ=13600 kgm-3 g=9.8 ms-2 Thus P=0.76 x 13600 x 9.8 Nm-2 = 101293 Nm-2 = 1.013 x 10^5 Nm-2
46
What does standard atmospheric pressure (or 1 Atmosphere Atm) equal?
1.013 x 10^5 Nm-2
47
What are other units of pressure?
The Pascal (Pa) and the bar (b)
48
What is 1 Pascal (Pa) equal to?
1Nm-2
49
What is 1 bar equal to?
10^5 Nm-2 or 10^5 Pascals
50
What is a small unit of pressure?
The millibar (mb)
51
What is 1 millibar (mb) equal to?
1/1000 bar = 10^5/1000 Nm-2 = 100 Nm-2
52
What type of barometer contains no liquid and is more convenient to carry about?
Aneroid Barometer
53
Describe the basic structure of an Aneroid barometer.
A corrugated steel box which is partially evacuated of air The top surface of the box is held by a strong spring S which prevents it from collapsing
54
When the air pressure rises what happens to the top of the box in an Aneroid barometer?
The top of the box is pressed inwards
55
When the air pressure falls what happens to the top of the box in an Aneroid barometer?
The top of the box moves upwards
56
How is the up and down movement of the box magnified in an Aneroid barometer?
By a system of levers connected to a small rod fixed on the top of the box
57
What does the magnified movement result in?
A pointer moves over a suitably calibrated scale
58
Since atmospheric pressure decreases with height what can the aneroid barometer be used as?
An altimeter to measure the height of a place
59
Where is the aneroid barometer used as an altimeter?
In aeroplanes by pilots to know the height of the aeroplanes above sea-level
60
Is the aneroid barometer very accurate?
No
61
Why is the aneroid barometer often used?
Because it is small and convenient to carry about
62
What is a faulty barometer?
A simple barometer constructed as above may contain some air or water vapour above the mercury column instead of a vacuum
63
How can you test the vacuum in a faulty barometer?
The tube is tilted if the vertical height of the mercury column remains constant (at 76 cm) until the tube is completely filled then the space is a perfect vacuum
64
If the space in a barometer is not a vacuum what will be seen at the top of the tube when the tube is tilted to certain height below 76 cm?
An air bubble
65
What are the two types of barometers in practical use?
The Fortin barometer and the Aneroid barometer
66
Where is the Fortin Barometer used?
For measuring atmospheric pressure in the laboratory
67
Does the Fortin Barometer give a more accurate reading than the simple barometer?
Yes
68
Describe the Fortin barometer.
The Fortin barometer is basically a simple barometer enclosed in a metal case with glass windows through which the mercury level can be seen at the top and the bottom of the metal case
69
Instead of the dish of the simple barometer what does the Fortin barometer have?
A leather bag to contain the mercury
70
Before taking the barometer reading what is used to lower or raise the level of mercury in the bag until it touches the tip of an ivory pointer?
A screw at the lower end of the bag
71
How is the height of the mercury level measured in a Fortin barometer?
From the tip of the pointer to the level of mercury in the barometer tube
72
What does the graduation of the Fortin barometer have?
A main scale and a vernier scale which moves over the main scale
73
If the atmospheric pressure is taken to be equivalent to 76 cm of mercury what is the formula for gas pressure (P) at A?
P=76+h/13.6 cm Hg
74
Suppose some dry gas is present above the mercury in the enclosed space of a U-tube manometer using mercury instead of water what is the pressure at B of the open end of the manometer?
Atmospheric pressure H
75
In the scenario of dry gas in a U-tube manometer what is the pressure (P) at A?
Less than atmospheric pressure
76
If the difference in the heights of mercury in the two arms of the U-tube is h cm then what is the pressure of gas?
P=(H-h) cm of mercury
77
What is a Barometer?
An instrument for measuring atmospheric pressure
78
How can we construct a Simple Barometer?
Take a clean dry thick walled glass tube about one metre long and fill it completely with mercury Cover the top of the tube with a finger and invert it so that all the tiny air bubbles collect together Turn the tube round again and remove the finger Fill up the tube again completely with mercury to exclude all the air Close the mouth of the tube with a finger and invert it into a dish of mercury
79
What is the space above the mercury level in the tube called?
A vacuum often called the Torricellian vacuum
80
What is the height of the mercury level in the tube above the mercury level in the dish?
About 76 cm or 760 mm
81
Is the simple barometer an accurate instrument?
No
82
Why is a simple barometer not an accurate instrument?
It can contain air or water vapour instead of vacuum It is also bulky and not convenient for carrying about
83
When the tap from the gas supply is opened what happens?
The gas exerts pressure at A and forces the water in the open tube to rise to a certain height h cm above point B
84
When the water levels are steady what is the pressure P of the gas at A equal to?
The pressure in the liquid at B
85
Since the right side of the U-tube is open to the atmosphere what is the pressure at B equal to?
Atmospheric pressure (H) plus the pressure due to a column of water of height (h)
86
If the pressure due to h cm of water is equal to the pressure due to y cm of mercury how can we write the relation using P=hpg?
hp1g=yp2g where p1= density of water p2= density of mercury
87
Using p1=1g cm-3 and p2=13.6g cm-3 how can we write the value of y?
y=hρ1/ρ2=h/13.6
88
Hence h cm of water exerts the same pressure as y what?
(=h/13.6) cm of mercury
89
Hence gas pressure (P) at A is given by what?
P=(H+h/13.6) cm of mercury
90
What three properties describe the state of a gas?
Pressure volume and temperature
91
How are the pressure volume and temperature of a given mass of gas related?
Through the Gas Laws
92
What is gas pressure?
The force per unit area exerted by a gas
93
What instrument measures gas pressure?
The Manometer
94
What does a Manometer consist of?
A U-tube containing water or mercury
95
In a Manometer setup where is one end of the U-tube open?
To the atmosphere
96
In a Manometer setup where is the other end of the U-tube joined?
To the gas supply

Physics (25 decks)

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